In what ways is the word “work” as used in everyday language afof(p,g )k5 tthe same as that defined in ptg ) oa,5(kfpfhysics? In what ways is it different? Give examples of both.

Can a centripetal force ever dh s:4w5pbuhs7+;ec e po work on an object? Explain.

Can the normal force on an6tih 9v/tl c9eq d9za 5r:c7hs object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doing 5ye gygx/oe:2 any work? If she stops swimming and merely floats, is work done /x:g yg ee5y2oon her?

Is the work done by kine +k oo:+ eup43ywjn//0 xorayrtic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under the pjr/0e4y+ooo+u: n xk3r ay/wm.]

Why is it tiring to push hard against a solid wall even thouadrr9 a*;s 5 ejwf9+oo 7r2wzkgh you are doing no wo9k+rad e;o57fjzr2*9os wwr a rk?

You have two springs that :-ro 4m pn(cnwevrle)zy: 0rpqgk 70lm(+z*u are identical except that spring l is stiffer than sprp +lzeo( erz4k:l0wn) c mg:nyurp *mvr(-q07ing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant1hbl /hspyc u 6r(r,o( horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a disc,p6b ohhr(uysrl (1 /tance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change when yb1 v,vw bqvd(jxjf4))ojv,bvvbd qw(fx)j4) 1 u jump as high as you can?

In Fig. 6–31, water balloons are tossed5gz..0g jght b7d lj1l from the roof of a building, all with the same speed but with j.g.gj1g07b lzd5l thdifferent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poin 1i/ *zr2t.wsjfad6qki7,s zht in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum 7ijwskz* s tf,16z qiad/2.h ris directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If3: gus/ro ,*1in*jtxy mwx4k p you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law up4j:*io ykr,3 s/ 1mx*nwtgx of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instrucgye*mi3,k8d .zzd/ z qtor pulls the ball back and stands against the wall with the ball against his nose. To avozzm,.ze8kg3*d/d q i yid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the graaje)xe a*z7*t vitational potential energy when water at the top of a waterfat aa7e)* *jxzell falls to the pool below?

Describe the energy transformations when a child hop .von ,kyl 1q;gha;/xds around on a pogo stick.

Describe the energy transformations that take place when a skiera grb+ wt1 vej :rx928rm46qul starts skiing down a hill, but after a time is brought 1rra+2rqt m49g8w:6xbej lvuto rest by striking a snowdrift.

A child on a sled (total mass m) starts from resg5 2cfk)tqd: *p;q k jppt,:jqt at the top of a hill of height h and slides down. Does the velocity at the bottom depd: * pkqpq tq;gp:c f)5kj,jt2end on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log io* /qw2; brnx,ull, gmn their path rather than stepping on top and juwru *2nlb,x/;g q,m lomping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, abl)coh7r f*s7cvn2 mf87* w mere fired into a bale ofc 7fh**28cr)w v neomlb7m7fs hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simpldp7bmz(5 q6euq1u)sg e swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grand m1sqezgd)u75u(q6b pfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its origin8 0ht8tp:*e)c5k gvvj-szjunal height? Expltujk:0scg8)vn 5 e tj p-h8zv*ain.

Suppose you lift a suitcase from the floor to fqg-h) mc:v8 v:aew9g a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along :v- m9 8wgfaeh)gq vc:a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powerg)nzzx /3,kpcqn5r 7r needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straighk0zqs*f822ucv huc)ft uphk uqsv 2cu)z 2c08f*f?

Recall from Chapter 4, Example7o/njiw) me6 h(+ c(as;bmnm28/wuazbvl5ai 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pullew/mw8livjne 7(i /muzc)oba(+b62mn 5hsa; ad up? Account for this, using energy concepts.

  How much work is done by the gravitationd8(-abjazs h;al force when a 265-kg pile driver falls 2.80sa(-bazh d8;j m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is rtr cqi*z((j k.equtqc( izk.*(rj ired?    J

  A 1300-N crate rests on thezhg lt0*;h (ve floor. How much work is required to move it at constant speed (a) 4vg(* teh;0hl z.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a mt;2vq /q+tjwfn:x 1k 160-kg crate 10.3 m across a rough flooj/m ttkw+; n12fqvx: qr without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fl0d: k0qbd;go02el jq3p/zox foor at a rate of for 7.0 s. Find the net w:0k z/0 j30bpe;qxd2 ogdfq olork done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kk/ 0y5 saby) f(basj-kg, lie flat on a table. How much work is required to stack them onj)aby -ssy(af/5k0kbe on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obj:3 slecw1(ue+ wvvpl(ects we might not otherwise be able to liff. Show that the ratio of output forc vws(w c+e:v1llep u3(e, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m dow5h g e:mf0s jw6ua22u+3dfxvwn a 28° incline and is kept from accelerating by a man ju:0gw e dxw52hsvf2u 63 mfa+who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a he,0e;d5 oiy lcdlicopter of mass M an acceleration of 0.10 g upward;dli,5e oy0d c.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is li3 drxx rilb1aq n(ue47;w.;tinear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting abyncb 4) (qujkab( 47hlong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) fj)uqb 7b(kbh 4(na4ycrom x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts dt 3*6l*ryjk4bt -jo ;qz,w cq ad kbk:-j6hz,in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecuq9ecec.a52 vy le, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubl 1x4puk2s 6 e nawoo)u rh1f7yk6qmh,)ed, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electrd k-j)v2)mj8nw;l21iyc alo ron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to st my/im0e9ye25,c:j zto8ww rtop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of,al 7djmfra 3n2 i87xj 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bo7fx a7,dm8r3 j i2jalnw?    m/s

  A baseball (m=140kg) traveling 32m/s moves a ffloeq,:*sk 2 oielder’s glove backward 25 cm when the ball is caught. What was the average force l,s2o :*qofkeexerted by the ball on the glove?    N

If the speed of a car is increased by 50%x(o0etk2ryr3pl ev- ym*d0(d , by what factor will its minimum braking distance be increl ev 0yr(r2d0deo*3p(ktym-x ased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s uh 31rn95r.nwifxie8 skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to bun35rnie 9 1r8xwfi.h e 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mztu 9cnd71fnb -m8og1v ;hwd7ass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the aver1n8w; z9f td ho7c7g1 vm-dnbuage force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown s nckgw. zb:g qm3,sk7s1x3 ;hatraight up by someone who does 80.0 J of work wc,33sxq gahmbk 1k: 7;gns.zon it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration2u*b e(swhc g( by a single cable. Determi*( bu2 (wcghsene
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness cony6x)e,jc:-iz6ggb v i+few 7cstant, k, of 440N/m How much must this spring bwey bj, vg6c)f-c7ig 6i+ex:ze stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thmhl0;.vgxs a nj882 wc4m9pvse change in potential enel;vw0 jnvg2p8m8.s 4h9s xm cargy?    J

  By how much does the gravitational potential energy ofoc -g.zwvi0wy9u h 6 xet5swsx*n8 28k a 64-kg pole vaulter change if his center of ma*-x 8xy 0v69 2kwsg wo 8siczw5uthn.ess rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 3bq0p .,opf pmkm/h when it strikes a ho,o3 p0b.mfpq prizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the:*p djdu,g ko7 ground so it is 2.20 m above the ground. What is the pojokgdp7 u*:, dtential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 3ow -y dfq9s;m;(s7jd 1uydw npse85x 1600 m and climbs to the top of a 3300-m wsm9uyy e3 jq (d;nx1s7 o5-d;fpw s8dpeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/mep n8u e-st1s h6d8p(y hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler1eneup(8s6tpdshy - 8 . If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) asro l q8o54xsc3m0 oe0u/ kit,nd grabs a vine hanging vertically from a tall tree i,kq40i rm /0os oxecots8 u3l5n the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starl5.tet2j;rcv4 m/vmk6 p xhs8 +9v icbting from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a s6 ttn.2gv8hr chove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed inmz 5 sqgv08 tpbd i(/ugo68lb-to gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar w0d zlt8( qv6gsbbgouim-/5 8 pith a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a 4 eehni *4e01bi4/mrcd .avmiplatform with a speed of 5.0 m/s1a 4eermiid/ivmb0 44e c* .nh. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffne6hsgph d7p9zknu6qfd :2,8 5w phyi0 pss constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg f6kn7 i9 ,gp6zp w8p0h:du2hps5dhqy ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction alongc-qwpp2suf 58uu*jmq uok1.8 the looped track shown in Fig. 6–39. If the blockuk* sq5qju1 c -u28pf w8omu.p is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spkaf7()ifdl z; ring stiffness constant k), Fig. 6–40. The block is given an initial displacem fklzif(; )da7ent $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bunge bp 8xj;y8h*l yz3pd)w3420xoyukyxhr3zf-k e cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constx k-j ybzu3w2khhx)3yo* zlpd4x8pf0 y3; ry 8ant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where it i2vp ikg 07v4fu p+vs3vs released frogik0+svv2p7v uf pv43m rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throwpz8+8j f aniws4c *y,dn with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the botlt-mkc7l0y)x tom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total masx )ktlym70-lc s of the elevator and passengers.

  A cyclist intends to cyclv x/ 3ry8luje4e up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each ofc5+f(tw-ui dt mass 7650 kg and traveling 95km/h in opposite directions, collittwdfu-+i (5cde head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wh+d;mk ra 7tjwh8. /biith a speed of 2.2m/s How much thermal energy due.ba7d tm hk;r8ij /+hw to friction was generated in this process?    J

  A ski starts from rest and slides down a 22:h zb ut5kf /6rg/b/ty;;aanx $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dro( ui i.ikw i*woaz 6k)n-l4sk1pped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from ah*zh-f - ovsj6 height of 2.0 m, and it bounces back to a height of 1.5 m.hosf-vhj* 6z -
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floobumie4 2nim i /uos)(4r with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the ne4nios2i/m) uu (bi 4mext 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a oktel r:cf89; /k7yhbspeed of If the average force of friction is equal to ont f/h;9 c7rk :byloek8e-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s rfdw/.y-go 7ivfi. rkbk y00 cdu-/ 0bkeaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attachedh 4bwqx78-ye x7 q.tnt to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kixtqn7.ye48 h7x qb t-wnetic friction between the block and the table?   

  A 280-g wood block is firmly attached t pjxotq06 o):bo a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of frio: tpqj 0x)o6bction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 krx kr)8, 8pfagdv .sx/g including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glidexx)gk rs/ d8vfrpa8, .r eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg i/ppnj 0 dh:;y nd*.)npj5)*kj wjskvpiano to a sixth-story window 1kp jdp*j:jy kn*n/5 )i nv.sdp w)h0;j6.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the avo-*)l7uqi;8d rpxvgc:p8v bverage force exerted on the car due to ;u i*ob7l 8vpv)d8 qcvrg:- pxfriction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. t*y,i, 8.qs ay1urvbql.3s roWhat is the average power ds,sa *u 1ioy q3qryv. .bt,8lrelivered by the engine?$\approx$    hp

  (a) Show that one British lea nb3+xq x5jg,p4 z613l dqmhorsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often :gk0b 2wpm/k5*f e dkgexpressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down f sz8pm.tvgk -5bdg4 l*rom to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a cok8m ggv.zs-4t5bd lp* nstant 75km/h.    hp

  How much work can a 3.0-hp motor do in 28hhfx rb2ofbk *6j6 p1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from 9 9i(pg2;)igc0hsscib n6epbrest to 14m/s If this motion takes 1.5 s, what average power was deve9 g6eb ihc2cb)p0sgni(;sp i 9loped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 mm)7hw/ htizv o4o)7-c ;z ksyj. What output rating (watts) should the pump motor hm hks-cwti7v;y 4zho/oj7)z) ave?    W

  During a workout, the c.it.,3jw((c cnx bpk football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an p wt(bxc jk,ni.c(3c.angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist clim wp+.my)2el pttdf5* xb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How3 io ytd3n6ryp( foy7(ra t*.+ke.ym h steep a hill can it climb at a constant speed of 75km/h if thymd.t+ erh. k *an y7(6po(3i3oyt fyre frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310- -frr;0 gqce9ru4bbr 9(r f*npkg box along a level floor at a speed of 1.2m/s if the coef rruf99b b; 0gerpq4rcf*-r(nficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0b8hbhqm/h;/ayav2ssgl9 4 j+;) oy4lmkby ( b $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars h(v sr6**zymn0d/ca;j1 p g rbaave built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assum*1 (av06da g*mz bp /cs;rrjyning the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the gf,voe z5u3x*h .zmjfqo * d/qrhw, 0*first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelfz* * / vq,q.mgh5ur odwxzffe oh03j,* holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in 3mnfsvi2 ac -a831wp 69hqs lkp+asz5the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. Whq pc h8mz+3s63fl-9aas2v ipsn5kaw 1 at minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown a;ks(+a0qoad2tuo yln i(y (zq:,( fxrh8ow 2in Fig. 6–39 is to remain on the track at all timlht f+yn82 yxad,a qo;( osiuq2k:oa( w0 rz((es, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft withoutmyo,ona5.q/wd jx 75e s(i1 nr his parachute opening. He landed in oji, w (1es arodn5mq.xn5y/7a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached tyvdbkvvz,*8a f)39i w ;wnw(uo a horizontal cord of length L whose other end is fixed (Fig. a)kvvzwyvfw8d ;ub*i w, 9(n36–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is i dx-(ye3v lr7bt1xo.made in 5.0 h starting at an elevation of 2300 m. yet .xi( v- 7xod3rb1lCalculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m+b 0yhq,pxdp j soi ench2:j2x9/97at above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in8s3ms.bny o -rqc/(y h California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neededb(ohs8y ycs3-/rm q n..$a\times10^b$ W a =    b =   

  Water flows over a dam a yeto:lm , ;rt+j+cts-t the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculat tjm,;c-rto+ely s:t+ e
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–1o7 kwp ce;wzxz(sg+ul 37rs3 fe/l;s44), the difference in your apparent weight at the top of the circular loop and the bottom of the circularrf glsekwo/ 7;s(ze lpsxz7c +1w;u33 loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar direqe4*s s, .eigrctly into work, how high could an 82-kg man climb a ladder if he were r.g,qees*4si fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle odrq5.h:ge-a. 9og a83xcdiwuf 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compre sd,p3 k:jr2q spisw51sses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on 1s rjk:pp3d 2ws5s ,qithe scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs )18k72bi bjjq+w j rej s iyg,h+wb36eat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his vebq3 gibbj2,7h+rws ej+6)ej 8j1 kyiw locity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athletekfqt )i4zze/:tdwpy mq h/ 8(/ climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output yzz tqpit/q8k4hfd )em:w(//was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped ts ony s+i44b:by reversible turbine putynob+4i ss:4 mps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k wto6n) )d;oml-i 5 d5zl jc+:xgl +bfris cut in half. What is the spring stiffness constant for eacgt5-wdon d i5ml;ojxl6zr)+ l+b:fc)h of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rs.kx 0iki 5q+iough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how lfk9osmf0js( 1fl -*zs ong will it take to accelerate from 55km/h to 75km/h Assume the power stays the sames*9m l1ff(zjso 0s-kf , and neglect frictional losses.    s

  In a common test for cardiayaek), e ua2-okz 2dp5c function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angoyk5dae-e2k z,u2 ) pale of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanlg0l opb.4*x tdp 0f9cce of 500 m, what was its velocity when it left the vl0l.9 xbgdo*0p c 4fptolcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a wate1 qqxq ,gx2/vm b)nczy0 jh6w*r wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what i,mz nvq)*qy/j whq26gcb0xx 1 s its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s