In what ways is the word “work” as useduw6icqjs8,z0:dny2vu m tw 3* in everyday language the same as that defined in physics? In what ways is it different? G,u*w zcvnmwj 0 6is8q3ty:ud 2ive examples of both.

Can a centripetal force ever do work on an object? , juj09zl ht54 dviq6wExplain.

Can the normal force oh7sne u0enm*) n an object ever do work? Explain.

A woman swimming upstream is not moving wiuz8zc:1g1 p5pn9 -x:vjli w ac(cz,cnth respect to the shore. Is she doing any work? If she stops swimming and merely 5izx pw9 ujc avg:znz,c1l: pc(1-c8nfloats, is work done on her?

Is the work done by kjbo)vja ,5.jkinetic friction forces always negative? [Hint: Consider what happens to th,vko )ja.b5jj e dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wa)+7 twbi 4zvetll even though you are doing no work?)tb+7vwi ez4t

You have two springs that are identicauwgc b j+ n;4qt0u7r v1.mpyqi2 vnl77l except that spring l is stiffer than spring 2 ruqqupc+l7n.4v7myv 1jg iw ;0b7nt2 $(k_1>k_2).$ 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 block that is free to ssdben5e 6 .nc)lide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has trave.ebend cs)6 5nled 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 much does your gravitational potential energy change whe tsi6, l4 *5i,6t l0/rvqt u-fhc+ ,tyqzozgcmn you jump as high as you c*h fcl q6tlz+ m-y, q/utz,it4gt,60scior 5v an?

In Fig. 6–31, water balloons are tossed from the roof lgm+ dc9xg 0gdyx,60)v zesh*of a building, all with the same spxl ge)d9*sgy6 d +, c0mgvxhz0eed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched zd gaux34.w*e w c1)vcfrom a point that is a height h above its lowest point 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 is directed upward along the trajectory, and on the second launch it is directed downward aloc1.c*egw4 wvxa)z 3du ng 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 3v47edor bvig)wv. ldb oq7 ,k6 yu(e)table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of co,uqrv)6d diokbewgbo7 l7 v4(v3y) .enservation of energy.

A bowling ball is hung from tf(w47ol*x8o92fs :rogl gi(t ykjm8l he ceiling by a steel wire (Fig. 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 ball without7lm2 w8r xf8(glgy(9ot l4ko:s jfo*i pushing it. Why?

What happens to the gravitational potential esek2rwum+u, 07 fn ljqua9*x.nergy when water at the top of a waterfall falls to the pool belowmj x+7a2 f quk90sle*r.w ,uun?

Describe the energy g a)7--8b:xb ecnvkja38vc yitransformations when a child hops around on a pogo stick.

Describe the energy transformations that take placlbjay+p3 ;k 4jbhy. f*e when a skier starts skiing down a hiabk;jjb3 p4yylh .*f+ ll, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total g b+0k 2.**rilruxu gymass m) starts from rest at the top of a hill of height h and slides b* lukgi *ug0+2. xrrydown. Does the velocity at the bottom depend 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 prefera/hg)c/mg cmj41 m,ha to step over a fallen log in their path rather than stepping on) mh g/gm/mhaca1j4, c top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the oth t0-v.w,j)pa vn ttd8rer, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arr.dnawv, 8ttjv )0t rp-ow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in termsd,wigyd)prz )r+ gt 1: of energy, (a) ignoring friction, and (b) taking friction into account,) )yzi+drtd1wp grg:. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its origi,b( k0 :)i*juhpauxarna ,ikpu *(ax:haj0urb )l height? Explain.

Suppose you lift a suitcase from the floor 2m.xcwz + gwng9eh-+qto a table. The work you do on the 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 weight of the suitcasezeg+ n g.h-x9 2mcww+q?

Repeat Question 22 for the power needed r.7ig nxm(4hmy ather than the work.

Why is it easier to climb a mo 9vs dl3r1qo:tuntain via a zigzag trail than to climb straight up?o1 v3dqls:tr9

Recall from Chapter 4, Example 4–14, that you can use a pulley and ro,s6 9hj/.+f 1b a kwxtc)0v;b*ehyroqblvu x6pes to decrease the force needed to raise a heavy load (see scx0olx.b)k/hr6ub;j hy vv 9a bt1,*fweq+6Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force fcm/mhlz4zljt ;1*/ o when a 265-kg pile driver falls 2.80 zm c//;1m4 o *fzjltlhm?    J

  A 65.0-kg firefighter climbs a fldu u9:7gh - n*u et2gg9lzus*oight of stairs 20.0 m high. How much work is requir gs:tl*u7zu oe9*2ung9g -uh ded?    J

  A 1300-N crate rests on the 1y2u v,7jqxcfh m06v vxds6. ka4pa3ofloor. How much work is required to move it at constant speed (a) 4.0 2qa1 p6d6fayo.scmk 4x3vuj0vh7x,vm 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 (lv:lc4 3ysvh9/md+ s vhorizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration,scsdyl:l3vhv4 +m 9/ v if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rak 4ti*3txc6 k a o2(o5.lrycofte of for 7.0 s. Find the neoyt.i*5ck 6xotoclf34 kr2a( t work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat oghb. ugv m:2jlu:ko.px d 1o9 9wukx4lg9;p1f n a table. How much work is requir:o9og2.dp k9 : x wbl14glhg;m1xfuu j9u.k vped to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we o+/ wsg 5jvw2pmight not otherwis5w w/osjg +2vpe be able to liff. Show that the 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 from accelerating bunvpd,u :/ f)zfrpr4 + j57qmqy a man who is pushing back on it parallel to the incline (Fi4f u,q: muvfprjd) 5q+ nr7/pzg. 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 acceleratp) do 9p*wfnf3ion of 0.10 g upwnp ofp)* f3dw9ard.    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 0)4w gw)r za q1dp*u4iyf1 xrj g1rn7a+ijs+pdistance axis is linear 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 along the x a8j jq609uwagmxis, varies as shown in Fig. 6–37. Determine the work dgj0w8mua6qj 9 one by this force to move the object (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 particq4h6-zdm k hf3ult g(-le acts 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 moleculdq/b/(w ;bzti e, 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 doubled, 0fm1c+nn cf5d 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 elet4 xvfugmq 2*/ctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 1250-kgcar traveling at 105h 2k.a)qyw)sue viisg7(8e.q km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow iyv9w ( hhm19 qy2hi8xwhose string exerts an average force of 110 N o9iy h8hw q( x2hyv1im9n the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove xur x*i2g9jw3x;g9.j+rcg9hnf59or qang7 qbackward 25 cm when the ball is caught. What was the averagx;xhwa9x9roqgn73g95g9 jjin r. f2gr+ uqc*e force exerted by the ball on the glove?    N

If the speed of a car is 3vnbk,hc*, )en gkky7increased by 50%, by what factor will its minimum braking distank ,v 7n*cgek,3 hb)kynce be increased, 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 skid mark t( cojvjh53xxe ,u6bd8 o be 88 m long. The accident occurred on a rainy day, and the coeffic ,x 8hj65od(xeuvcj3b ient of kinetic friction was estimated to be 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 mass of 0.25 kg is pitched at By the time it reaches the pfbxnda fd2v ; 2svo:heae9874late, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, i8; 42xobveeahsad:2 n9vffd 7 f 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 who 65acjs; *zgh9peu yxdi2 z(3ta4;mw o does 80.0 J of work on it? Neglect air red9zz w iajuah6xg2o(;p c 5ye* 3tms4;sistance.    m

  A 285-kg load is lifted 22.0 m vertically with tx fiy(r qi3ou :;em8tuqu/1 )an acceleration by a single cable. Dt:(tyum31xi8/ foiue rq q u);etermine
(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 pbgh4 gl5t. r4uk6 /zostiffness constant, k, of 440N/m How much must this spring be stg4.zbg4r6 u /hk tol5pretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highe2uqmb9ym y 93br. What is the change in potential m3b9yb92 yq umenergy?    J

  By how much does the gravitational+i )yzjn 7yr;13jh use potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0yzs)+3 ;1 u7rijejh yn m during the jump?    J

  A 1200-kg car rolling on a horizontal surface u o2k e z3d-g+kd)2tma 5zch0ahas speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. g0hk 2cd) oktzma 5-2aedu3z+ What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg boo...ajb m( olzawo5g1hk from the ground so it is 2.20 m above the ground. What is the potential enerwl zo5o h.1ag.bmaj(. gy 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 1600 m and climbs t:wfyc gyd xc07(kj2v0lgb1 u8 o the top of a 3300-m p2dl7c cbg0( yg 0jw8:1kvuf xyeak.
(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 vertic p6c: zg8ftlg2-puy. mally next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. Iflcpytf.-m82u6 zg: pg 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, izrsm:y;dpy7 :joo +) lzz)o (is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing up )yz;lji :dyoz(zro:)o ps7m+ward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from resxcwax3nv )+e5 t, 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 giw5ingbon4p ;l ;r+ d,gven a shove 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 kinetic8wyrnh-yd ( 1l energy is transformed into gravitational potential energy without(hw1lry-n y 8d 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 vertically ue 9x;2c;qarrd 7c dfc7rxu 4(dpward from the top of a platform with a speexra;cru9fc77xcrq 24dd(d ;ed 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 (ignore its mass), whose spring stiffness constant *wpl3k66wd6i4a 7l+/ vavx gqs f78a ymhy 8vbis 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it g l6 6pv hala8da4six7 vvyq6k*3+ 8fb w/7wmygive 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 Fisj-z3 luv o:* ubb8pf;g. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), frop;fbu u -bjo8s:z3 *lvm what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffnesa2ju76cxo q.ndlt6ra 9+ itsxi o)kv7 m1pr0/s constant k), Fig. 6–40. The block is given an initia0aq72 xtkand l/v.7)otu +c r9mxri61io js6pl 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 j*t57 zp oc(yswly7;* zxjo 2ywumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring p2(y7 z5tj*zywxyo7; csol*w stiffness constant 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 ss2wxgti- )gp;2r sh j;hown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the j;- htg2ix s)sg;r 2pwspeed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s f/7u)mjkad,vo p,aq 9 or0jr r)t l+,aat 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 desig7 )88alnhr npq.g5kx,tqrke :ning a spring to 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 5.0 g when brought to rest. Let M be the t5 hrna, l kp:8qkx.)n87grtqe otal mass of the elevator and passengers.

  A cyclist intends to cycu)l 9/ya (j5ps)atkhzle 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 travel a;9y.7 lb(0 ugyfwkcling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? byu(yfl lak 90;7cgw.$a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speed v, 8 +h* n+k-b,a qwmrft dvy:llfkr*-of 2.2m/s How much thermal energy due to friction was generated in this process? - vnlv*tk fm,w *,l: ydbhak+-rqrf8+   J

  A ski starts from rest and slideud 4m2yx,/nmxmk.v r0 s down a 22 $^{\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 dropped from a tree 1wl:)96l db,n7efe0(i re ha ve u6gzf;3.0 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 bounces back to a height of 1.po8f qa;;uxp gm)5 bsff(o* f*54y dvg5 m.*yf vodmf 5(a)usgq;; bxo5p f8 *fpg4
(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 apyvzr2*n;e a9y.js-.m l/c vacross a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the ep n.-as*/ 2 avj.;z rycvlym9next 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 wid r49rwasb kc:e1bn 6ce,jv8/b7bvd *th a speed of If the average force of friction is equal to one-fifth of its weig8 /1 69 :bkcewvsbacd7*bjr v4r ,nbdeht, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s rxq6jcwtj*ou9ai 9 u6,eaches 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 attached to a very light horizontal springhz /xvmjufbo/)(.y a) (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system,)yh (zouvj.fx )a /mb/ 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 kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a z7im3) pw w*x. 0-8rye 4ry2hp3im makekkm+svery light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A for ip2k0*m yaeskz-xem 34pmir.ry 7h w)+8k mw3ce 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 pz5,o zgx2ey4 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 ,e2pgxozy54 z 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 /g pdmu;+),(qp ( fecr pzxp7ba 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 eq7( +zd g pp/bfrc)mu;(,xppm above?    s

  If a car generates 18 hp wheyfh 3u3qb6d -qg9 os6ln traveling at a steady 88km/h what must be the average force exerted9 yusg b6-f6dqql3 3ho on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the averaw qx;32r qr+i(:lnpk4yey 0a:oeilp4zp *ci 6ge powel nic( e;4yq6+rorp xkq:a 0i2w l4pi:*pzy3er delivered by the engine?$\approx$    hp

  (a) Show that one British horsetx*mp+u1ii1 s power$ \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 oft *ez 8kc.r4bjsy,2tzken expressed 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 hkefbbv +zpv 3w 9v dss++9+*leer 1150-kg car slows down from to 65km/h in about 6.0 s on the leveefbk vedvs 39vb++l z*p+9w+sl when it 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 m:. hgk1vk, aj8bp-iva otor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motiotol9..wxw l- r2eg)lfn takes 1.5 s, w9-.go2 rl.wlfletx) what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of wat 2gtl2* jzv )jeioye.;er per minute through a height of 3.60 m. What output rating (wattyi gv.2jz * )elo;2etjs) should the pump motor have?    W

  During a workout, the far:w,3 fpa ;liw21de pootball players at State U. ran up the stadium stairs in 66 s. The stairs are 14fwa3 ,iawp rd;le1:2p0 m long and inclined at 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 climb a 61hj8 8ytwv.nef 2seoay/4x. lt f4yc4.0 $^{\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.m:oa:f1 6iwuea:ua r, fooz(7 ;di;co How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add ufoo7ador:1;ui moau,a: ce ;6wfiz( : p to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able 2t+k4nddu d 1xra4s- r64 ymdnto drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient da4y 6m-rndn t4 4+x1kdrd2suof friction is 0.45?    hp

  A bicyclist coasts down a 7.0g (7dr0ei6o o1qq5o)o i 2t-wdr zxg7n+6agd h $^{\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 hnz/ b il po0(kxn-,5/g:qgc p0qjwon4ave built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damanokbg:z04-x 0g(jp 5/w/cpinnql ,oq ge 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, 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 -ro 4abzi04y i/;s cicshelf 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 hasi/rsicy0 4- bz ;co4ia 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 19 u3jwxf4 kk ,e9e(*mdg36 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top o 4kf,mxgu(k*j 93 edwef the arc?   m/s

  The block of mass m sliding without friction along the las;o/pt*cy 6tooped track shown in Fig. 6–39 is to remain on the track ap / asto*cyt6;t all times, 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 witho1yi s;9rt m v0ay9kkmu;3ngjs7 m6ok1sj:o1out his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survi7 m tosmi91;3 a6s0v: k1;n9s1y jgu ykjokromved 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 cord of length L whose other end is da :0xb;2kpp :m7rfvno kzc24fixed (Fig. 6–43:a024rpd: 2m;vkfnpbo7 kx zc).
(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 y7o f;i) f3djra 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate jf)r3o y; ifd7
(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 above a huj2nm .*p y/;,sbn fjt6gl1tisge 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 4jf4sh(g1 8qywxe r9-+dc4hxc j-y vs +7,000 people per hour. If the average lift carries people abocv8-(hf xjxe+-cgrqsy hsj+w 1 44 9ydut 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 and falls verticceaqa6)*43su)z q aeb ally 81 m before striking the turbine blades. Calculate qqsa* ab)zue4a) 3c6e
(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 loops(kboi:63o zrw 9 e g:+lzr4se+.nzmr (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show al3r:bw4+.zl:zi(ms+6gnze s9r rook e so 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 coulmdiwt3b (y 7l2d convert a candy bar directly into work, how high could an(2tld3i7mwy b 82-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 92u.cq cuc,k2iiv49u8,6)jvzxu pqy+ngyguan upward 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 scale compresses 0.60/gj jrk7h3 p6o mm, and it tells yorphjg k7j36o/u 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 swiaqw/ vt9ip8h /ngs out over a lake (Fig. 6–45). He r98i/t/ h wavpqeleases the rope when his velocity 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 of 5jk+*vm0fy ; zf3k6otx+ e/lse.0 m in 9.0 s. What minimum power output was used to accoskem/yxojt ve0k36 z +*fl+ ;fmplish this feat?    W

  Some electric-power co7:r ddr.lop0 *ylep/kmpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a hipledpr0k/7lo :*ry d. gh 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 is cut in half. What islw ,n+fbc j/u rsw:13b the spring stiffness constant for each of the two resucljb w:3,u1/wrfsb+ nlting springs?   k

  A 6.0-kg block is pushed 8.am*;axqs/ sucx; )8wb :fk.kn0 m up a rough 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 from6c*f g12nkdu* m0sjl h 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, gkl6f201 md n*s*chjuand neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), t twh6bd7,mw1mn)(e+ xdeh xg+he patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patie6(b wt)d, w+xne hx7hd1g+ mment 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 spewa/8 36la62kbr+ksjok zs tq* +upgxh8s a 500-kg rock vertically upward a distance of 500 m, what was 2as azpg ql* 6kk/6su+b8r+j8ok t3hx 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 9me6yb6rn- xg 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 is its maximum po6- xberng6m9ywer output?    W
(b) What is the speed of the water as it hits the wheel?    m/s