In what ways is the word “work” as used in everyday langcuv; bqh e)g5td /5t3euage the same as that defined in physics? In what ways is it different? Give examplehqe5 t 5;gbd3) /cevuts of both.

Can a centripetal force 0.u upd4dn 6 dc/zth,yo/z;ijever do work on an object? Explain.

Can the normal force on an object evpvx 5n-ixy+v y5td :cu9.ro6oer do work? Explain.

A woman swimming upstream is n5cfm.sj5ohzt7 *1 w7 jvhew.qs +p e3iot moving with respect to the shore. Is she doing anyh.mo7te i s*h+qj e315v.5zfwwj ps 7c work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces a*red*)jru8 6shedhq /lways negative? [Hint: Consider what happens to the d) **6j8rd edh /euqrhsishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall t bm n);79f gn6 m6aq;pukcqfuldi3-(even though you are doing no won;t;fu cqbgqup m7)i6da f36 nml(- k9rk?

You have two springs that are idem(d7)aia3mkp8t y tq*ntical except that spring l is stiffer than spring t8ma mda*3(y pki)7tq 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 constant horizontal force on a blocm 8bf6zwmi3wjh - .9abk that is free to slide on a frictionless surface (Fig.6-30).b6wwf mhj 93 zabm-8.i The block starts from rest at þoint A, and by the time it has traveled a distance $d$ 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 ixt,ge0d88i cmuch does your gravitational potential energy change when you jump as high as ,icgitx8d e08you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, rr89cs q7x6opall with the same speed but with different launch angles. Which one has the highest speed on im 9rr qopx6s7c8pact? Ignore air resistance.

A pendulum is launched from a po*dvz90hehgyb4j,h:: nf g h x)int that is a height h above its lowest point in two diffdb,*h xhy: vghejh) 0:z4gf n9erent 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 is 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. If you compress 4 a/3cus gomn)the spring by pressing down with your hand and then release it, can the spring leave the tac s)3a4/onu gmble? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Figq5hwe 8;5ir q8v 717ujcwkrvg. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the balc8krj7qigwre5w7u hv;8 5qv1l without pushing it. Why?

What happens to the g/: vt(nesj;x1oqvi9 c ravitational potential energy when water at the top of a water/:x; ce9t1os q vjnv(ifall falls to the pool below?

Describe the energy taa*x* 70u9iha l*3 aeofb ffh,u* /dkoransformations when a child hops around on a pogo stick.

Describe the energy transformations that ti.w*vgl/ lh,kt-yv w3ake place when a skier starts skiing down a hill, but after a time is broughtv-tlwg 3liy. /*wv,h k to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest an bl:z* +5a; :q3wchhbml 5tqxt the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no frictiol*whq5zb th c5:;3 mnxblaq:+n, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log91n n9*bzu do )zya-pw in their path rather than stepping on top and jumping downy*bpow9duna)- n z1 z9 on the other side. Explain.

Two identical arrowsyuaj zs/(q 4/o, one with twice the speed of the other, are fired into a bale of hay. Assumin yo/ujq4(s za/g 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 simple swinging pendulum in terms of energy, i84ut+vh dyxz f. (fb2(a) ignoring friction, and (b) taki+vfh.4fxb zti yud82(ng friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebounh.ux2 4j-g9 n jpdofnk2cku/n);tg 1ad to a height greater than its originald2u. np )a-c 4 ghkjgxfko9/ 2nnuj1;t height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on t0x0/o7 ahemx ghe suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the xemx0 g7/0ahoweight of the suitcase?

Repeat Question 22 for the power needed rather than t1izpu5gm- gokq fyyo)h82ob6a -i*u8he work.

Why is it easier to climb a mountain via a zigzag trail than to climb strair/ ogpc:vk6hu0oy( 809 n uolyght uy0hocl: 6o(0r /u8nkgy u9p vop?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dngxkv0x9v* xni l,vt(3xek6 )ecrease 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 pulled *( vvke39)vxnk6,nixtx g x0 lup? Account for this, using energy concepts.

  How much work is done by the gravit:y bjxkt,7cgabw w;y5 1aq,k +ational force when a 265-kg pile driver falls ab w5 jc,ktwaykqgy,:1 x; 7b+2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20,xk/* zb55p sfz )9e0 ozlpnkq.0 m high. How much work is reqzfbp*nkz5 x)skq / 95,lz pe0ouired?    J

  A 1300-N crate rests on the floor. Howkfklg/6h *;nzzi yqoc8 ):1o z much work is required to move it at constant speekig;k)z8o *h:o6y 1/ lzcfzqnd (a) 4.0 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 160-kg cratw .r - pfmcmsj,i41mu1,i a4pie 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50? mjrm1,a,m p c1 i.swpii f44-u   J

  A box of mass 5.0 kg is accelerated by a force d8 (xvd1r/f2yuql :;e5 ddiwa across a floor at a rate of for 7.0 s. Find the net work done on thewayx/8 r(5v ddeildud2 f 1:q; box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on;y8cnrwn ps*+ q 2+zga a table. How much work is required to stack them oner;gwnapq8c+2ys z+n* on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we m;cj7*q4wr c5 xgrl/cw 0ha vq.ight not otherwise be able to liff. Show that the /;.vq ch0lg7jc5racq x4rww* ratio of output force, $F_{\mathrm{O}}$, 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 down a 28° incline and is kept frooa ,,(,lyf9w x5uuw va)l jua1m accelerating by a man who is pushing back on it parallel to the incline (Fxuu9f 5( ua l1vaw ,)ol,wjay,ig. 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 helicopter of mass M an ,2myz8p f4g6+lz9 vwuo iwp,cacceleration of 0.10 g upwgo6 lc9+pw4 uvyp,8i,w mzzf2ard.    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 linear ory2bj rmq9o 3af:82 hand 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, actik6bulj 5 jp .p;s,rpa-ng along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objecpsr6jbpj;5,upa lk . -t (a) from 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 /fxpzv 0gg i09acts 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 molecule, with (88ipsyzen,n 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 doubled, by what factor has its speed increasdd (o q6tr4k0da/f/zv ed? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an -*1 qoqj3(pq j6obnt xelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 stop a ty)xvrv2x a7/nl (hcw5g18h n1250-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 a.ac4 r6pet7te verage force of 110 N on the arrow over a distance of 78 cm. What .ee pr4 ac7tt6is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelin, uonxtu:8g:hsp:vt 1 g 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glotn8u::stgv ,pxh : o1uve?    N

If the speed of a car is increased by 50%, by what factow(1za6oomjuvon8 /)k2 nz:e hr will its minimum braking distance be increased, assuming all else is the same? Ignore t wh2nn()86e:vz1koz uajmo/ ohe driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark :pdh/t9ji/1ok-obqb)ur6vf 9eq 3dnj ,ixt- to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the drivedpnt v1uxki9j oq 6i /o)/ jdbr-9tqbfh,3 e:-r slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.5b3wm t jr8zn)25 kg is pitched at By the time it reaches the plj3twz 5rm 8)bnate, it may have slowed by 10%. Neglecting gravity, estimate the average 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 straight up by someone wn0 s1 1 ejo-*d)6sgvmz, uhwvwho does 80.0 J of work on it? Neglect air resistance. d-o0g*z n,jsm1se ww1 u6h) vv   m

  A 285-kg load is lifted 22.0 m vertically with y,wrr lmu 82u.an acceleration by a single cable. y,.rw82 rlum uDetermine
(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 constant, k, of 440N/m How pjbfl h j5/fvjk+2z; *much must this spring be stretched to store 25 J v +ff5*jp j jb;zl/hk2of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hd5fex 1,zpiz+w*v jb3uzbx5 jj2 z +r-igher. What is the change in potential energy? x *3+-p ,zrw jxfj1z5jbuv5i+e 2zzdb    J

  By how much does the gravitational potential energy of a 64-kg;ovbeugesy/bf uo8n c*(8e x:2+pu0 x pole vaulter change if his center of mass ribe8 nbs;e+ (youe:cxg upv/2o*f80x uses about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sus tyxb 6if68 fks;if5(rface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in6s ;5kti6sxbyf i f8(f 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 ground so its l+.ii 0gej)y is 2.20 m above the ground. What is the potential e s. iiejlg+)0ynergy 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 16cs,erugle ks tk m+ 3)c3o;qcdqb.(/. 00 m and climbs to the top of a 3300-m peak. kb.g/ cutk)+oq (se3 c3cq,m.s;eldr
(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/m hangs vertically eo)b+4dmr+fd hulf8 3 next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where wil+8d mdlob4+ue f3fhr)l the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runnine+k0d*bg2waa: ,hbb z h3f5nog at top speed (5.3m/s) and grabs a vine hanging hebzbo , 5na g*a3b2wk f0:dh+vertically from a tall tree in 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, starting from rest, slides down a frictionl co 7m;*kx/ztqmrj0t4 ess 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 shove up axido2.d5 2kxm9 *qydo 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 ion nvljp o8 k6f:oil4(sz52i(nto gravitational potential energy 4( (:5i ofop jvsnni6kzl2l8owithout 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 with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertu,4a0ep + ,6yfxmbs,b..wo99cl qz iect( qmr ically upward from the top of a platform with a spcm pts fu6a bx99woyrl,q0i zc..m+b,4e e(,qeed of 5.0 m/s. ($\alpha)$ 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 (i uevzu-w r8mlm14 l/ob -q o/5g7plbr-gnore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed dowp e/785o-muml-z 4l- lvgq1/ourbbrw n 0.150 m. (a) What upward speed can it give to a 0.30-kg 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 along the looped track shown in F1dssna( xr1z:m8sch vw z.(; (fas* rtig. 6–39. If the bloc sd(wa;ar:fzzvrt.1s s n8h1 x s(*c(mk 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 (spring stiffness (5mtg/a /ruj c.dc c/ivp*a; yconstant k), Fig. 6–40. The bloc/c*;tc g i ( jracd5puay/./vmk is given an initial displacement $x_0$ 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 bridgehpyu 2 ztg0 86 1;u vmv0s67qbkpzb2pl. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee colqzp6p 28bbvymt2uuvkhg0z s1 p67;0 rd, 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 po.c 3dw 9u zdid1e4,yvbint 1 where it is re bd d3wi9dceuyz.41 v,leased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 myk q/ j4 gooj-;2pa q3)uyrn4c/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 y0 :bedqhd bj3s-)ir t+(;qix be placed at the bottom 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 -0ey 3+i bq;hxs b(: )jrdtqdi5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycl(jzgy iz5kdwq;os/le6 2r*.m e 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 of mass 7650 kg and traveling 95km/h in opposite direc0 glyv wc:-6js(abkn;tions, collide head-on and come to rest. How much thermal energy is produced in thl 0w6yas bgj(-:knc;vis collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches th) z7n1a mp(-0h(bwmte ncsod;e bottom with a speed of 2.2m/s How mucd1n( bme st(mhp;nw0 aczo- )7h thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22 8.a3a--hcuzje x h2us(unqf1$^{\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 dropp .n,mij nj* x((b4kdzm yse 4zl/vx3.bed 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 a height of 2.0 m, and it:bg lkd p208z1mids l+ bounces back to a height of 1.5 m. 2kmg+lp:d l0d1zs 8ib
(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 fvb 5 as6*p-dealoor with a constant horizontal fo5a-vae*dspb 6 rce of 350 N. For the first 15 m the floor is frictionless, and for the next 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 speed of d9a4;a1gce0q9v mxep If the average force of friction is equal to onp 9 cxea409;ev 1qadgme-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 reaches the foot of a3t53qqx ea yuc5/fhp, 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 attached to a very light horizontal spring (ku,vu xadtu r.a9(5 mmz3o(3et=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and relet.(u mtua5 m (vxdora3,u3e9zased, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attach 3+5pauan;s7z7bls h ted to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction 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+7a5lzh;n7spt ubs a3 on its first swing?    m

  Early test flights for thefsx6kp0 rsi08 space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have fs06xr8kp 0is 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 takl1jbkc8s+)p/p z/dn n e a 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m ab+ d)zlbp8/ s jnpckn1/ove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mu-y:vv.bap/kh i2qcb )st be the average force exerted on the car due to friction av h:bqyk.2cba -pi)/ vnd air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is 5lo0zf u 5/ckc*, rijfthe average power delivered byo uf0*, lczjrcf5i5/k the engine?$\approx$    hp

  (a) Show that one British horsepowe1e5 wib6y mps se,hr53r$ \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 expressed in t7lm1 +9gmx0 *bcsfy gyhe 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 downb xf;ewp1w+ e9 from to 65km/h in about 6.0 s on the level when ; w1 +pb9ewxefit is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mow xx* :i k-t:lso(pw4ft 4jbo7tor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kx.2 e1d-quytz7 w *phkg shot from rest to 14m/s If this motion takes 1.5 s, what average pouy1.t -e*dh2xk z7 pwqwer was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wht+u-p h ,die:x,m9kksat outputx p:te,ks+k h9- udim, rating (watts) should the pump motor have?    W

  During a workout, the football pl c6hmbiu:-cn.xhcgi i ,-.n9jayers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined atc.-.hcunx,hnb: mig-i jc9i 6 an 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 k wdh poc ,38(+wtybm-climb 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 m:l1cqqx + j /lpp)r.njaximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 )jqjqrx:p1.c l+/n pl N?    $^{\circ} $

  What minimum horsepower must a motor ha7 +; td))vdsio /of(k oc/mlkwve to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictiododkc miw+( fo;o 7/l t/)skv)n is 0.45?    hp

  A bicyclist coasts down a 7.0:yvpro b,)s,(3 npn nq70+cgb,qnmbk $^{\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 have built “5mi/h(8km/h) b2 /wjkq,ov5cz umpers” 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 spr5jq/zv2c o w,king stiffness constant of the bumper be, assuming 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 first shelf is 10.0 cm offd)qk/u6118hhsx (n nqw yjl r* the ground, and the remaining four shelves are each spaced 30.0 cm above the previous ohk n/ yql(u1rs)dj 1hq 8*n6xwne. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf 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 the ):dvf9ort)30 cdf unb1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed ou3d:ncv)r0ff9 t db)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 in Figb( euhq (uu99e. 6–39 is to remain on the track at all times, even at the very top of the loop of he(ue u99(qburadius 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 jumpinr8eyih6d 4 9 nxg5ahmb vxp.:7g from an aircraft without his parachute opening. He landed in a snowbank, creating a cra9xpeyh bdr:785in6 a.g x4 vmhter 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 to a horizontal cor:7do1jkq pw4 v5vhz 1dd of length L whose other end is fixed (Fig. 61qw1j7 5dhpk o4dz v:v–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-hig,rcbzws -;tia *m,3 tlh mountain. The climb is made in 5.0 h starting at an el,ibst a;tm *lc-3wr ,zevation of 2300 m. Calculate
(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 af.gdnrl ;tp) 7ap24s kbove 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 in California claims that its lifts can move 47,000 pe (kvc08ncjn2wen9 ,lrople per hour. I,0(en 8wncvknrj 9 l2cf the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s a,l uv:/c uouq-nd falls vertically 81 m before striking the turbine blades. vcuo -,qu u:l/Calculate
(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. 6–44), the d( gwncbz(:5on ifference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s —gb(5 :wn(znco 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 directly into work, ho:;z,hg3x l6)aftd cv-ld3vwz w high could an 8a 3t dzh 3f wg)dclxlv-z:,;v62-kg man climb a ladder if he were 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 y14 ;njbppok( angle of 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 scalp*dxe (zy+trs*/ih5 v (cmdos/sb 2,me compresses 0.60 mm,hy//oi( vx bmc5+s ,*pms d er(std2z* and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swingpdkt * zrr 7ld6c+):bvs out over a lake (Fig. 6–45). He releases the rope when his vell + *:)rtbk6dpdz7cvr ocity 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 athlete climbs a vertical distance offh;prt y6b phu81mt 8( 5.0 m in 9.0 s. What minimum power output was used to accomplish this fe8bhf6p ;1ptry m(hu8tat?    W

  Some electric-power companies use o;/lk s xl uz,qpqesc7j3 1-(jwater to store energy. Water is pumped by reversible turbine pumps from 7jxu lp1sk/ ,qz ;o3e(-js clqa 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 +gjj8xgtr.+ ofe ),rb constant k is cut in half. What is the spring stif +8ej)gogjfx .+,trbrfness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rouggu,iu*f ;sh9 gh 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 55k 0pn7 kjk;g8:3 t4/ :gr n6l ylq5xowxdl0utbgm/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays 3gp;84l6wqtb07nudgtgkryj x/:0 nllx :5ok the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient w fjd )v-rr,c:cxt+sg +alks on an inclined treadmill (Fig. +srgx-j+ ,cr)v cd:ft6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle 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 vertics /n m7txj x4)eiuv:2lally upward a distance of 500 m, what wast7lie)x / js2muv4x:n its velocity when it left the volcano? $\approx$    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 water wheel from a heihpe9ddv2 1 8tsght of 2.0 m at a rate of 95kg/s (a) If this dspdve1t9 82h water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s