In what ways is the word “nso tm5q6hb 67work” as used in everyday language the same as that defined in physics? I5qm b76sno th6n what ways is it different? Give examples of both.

Can a centripetal force ever do wo.emhhrju-0f v) dyb;kl+:nj8 u h4t0v rk on an object? Explain.

Can the normal force on an object ever do work?8 z 27eycne js4vpfy0g4az(h * Explain.

A woman swimming upstream is not moving with respect to the shore. Is shhn 1ek/3q 5b y53)r mvzwwv(une doing qmnwu1n w/5e)b z yk5hv3 rv3(any work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwa5 cupesm- *dp:m-t.lp ys negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from : u- mel-*pts5 .cmppdunder them.]

Why is it tiring to push hard against a solid wall even thoug 859ar zof0 df+tmlis;h you are doing no +0a9rozfmd f5is; 8l twork?

You have two springs that are identical except that spring l is stiffer than 0h,yg s.p )5ogk7nhm42z wak yspr)k.s0kmgp7h wzn5,4 y oga 2yhing 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 constanjz1wv45)l dglkh ad50o.1 tr it 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 hwj o1zdt54rl. 1g5 0a)dikl vhas 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 much does your gravitational potential atc;q r,jw p:,*ej k.fenergy change when you jump as high as ypjj arf,*q. ,;:ck tweou can?

In Fig. 6–31, water balloons ar 6n 9q)-zg7xvnut0lewe tossed from the roof of a building, all with the sam06ne ulgv )xz9t7qw- ne speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launchedsrv ly3/rk ( 0ad o/7u36-o9m qluudsd from 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 dirl o3dm/ rd 6q-au/yuuks(73d9oslr0vected 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 (vh nda 8bbs5vb.j *2/ltf*:ou *e xclthe spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.*uj sh/ 2ea 8bt5vdlc*v.lxobf :n(b*

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instr+ ay0sn8s zun1; vh.icuctor 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 without pushi y.zna8 c;vhs+s1i u0nng it. Why?

What happens to the gravitational potential energy when wa2y goj9b5q ;p(u +bwjeter at the top of a waterfall falls to the pool belobu 5+gp9wbje;( yj2 qow?

Describe the energy transformations when a child hops around)iuu6lz (a/v t on a pogo stick.

Describe the energy transformations tml qz-)6aorl; vqz2,se,m -r ihat take place when a skier starts skiing down a hill, but after a tim,rz,2ve zmrim-l 6a)sl-qq ;oe is brought to rest by striking a snowdrift.

A child on a sled (tot8odbi2h.;d/mz(x /m98h pl-xv fvh ho al mass m) starts from rest at the top of a hill of height h and slides down. x;lh8dipd x /homvb(82hz.hv9 fom- /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 prefer to step over a fallen log in their path rather 92psx4c i (vnz,r9 ssmthan stepping on top and jumping down on the other simss99xrnpi(,z2 v c4 sde. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a b3+mzv9 fclh9 4dh-pcbale of hay. Assuming the hay exerts a constant frictional force on the arrows, the +z 99- pvcd43hcbl hfmfaster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinghknl y8e s:f*g7 xdz0)+e 0dpning pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatgxdd)kezp0 es0*l h:ynnf7+8 her clock has to be wound up.

When a “superball” is dropped, can it rebound to d ut2 ,k8*3wtr9 jj:rjgyp:spa height greater than its original heightju, :3dw*s pj 8pgry:t r9kt2j? Explain.

Suppose you lift a suitcase from the flb7a v i+60vh//h1p pu q,cye5ynhu2fkoor to a table. The work you do on the suitcase depends on which of16u+by /pkvq ,2/5 ae hpnihch7vuy 0f 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 suitcase?

Repeat Question 22 for the powef,ynn a) tmv )vb dvo;7of+b+8r needed rather than the work.

Why is it easier to climb a mountain viamyuvwx.zx .2q7hnn/+7kbggeb2 *a( z a zigzag trail than to climb straight upu z b/(aqh2yz x k7e.27+g*bgnxvnw .m?

Recall from Chapter 4, Exam:g,q8 /hozvl*mo9+ixk sjm9bple 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Figm9l oxizq/gm:k ,ov+sh 8 j*9b. 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 gravi4, x0w 6hgwi dr-hc1wyvow k()tational force when a 265-kg pile driver falls 2.80 c0g-) kw1r hw, 64vowdyw( hxim?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much workg6q(0;k zpj)et m iu2v is required(qi6z;p tg0uem jvk)2 ?    J

  A 1300-N crate rests on the floor. How much work is requi+b85bs 8e 6jan6lbhhjred to move it at constant speed (a) 4.0 l 66ehsj88jbhnab5b+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 (horizontallom juizm )7 *l0qhl(a4y) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the eff * u7i) mmql(h4joza0lective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by4w png-7fa6wh)/xwb 5bmh fs, a force across a floor at a rate of for 7.0 s. Find the net work done on the box.fhmw5awf, 4whb-b /x ns)gp7 6   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How uc5,8awc4po9hm 33g roqgv;.x 7qaxk much work is required hr 4q3p8gcvxxma7 3.o9cowaukg;q,5 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 welua6 ; 3:exucb might not otherwise be able to liff. Show that the ratio of outpu xu6lue3 a:;cbt 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 accelp+s -uwf)yhe, m 6jls+*b6 yxferating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0l ys-j )u6+,*y h pbsfx+6fwem.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 helicopt k3*t :swbh*e6 jol3kjo6 dbb1er of mass M an acceleration of 0.10 g upwh lwbk*s:6jj3od k1e 3to6bb*ard.    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 and thatafw;zqzw bf8s z,+y8i,,qg 8v $d_{\mathrm{A}}=10.0$ 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 axis, varies as shoud0 pjtg /xstfp (- 8i:qys:l+wn in Fig. 6–37. Determf/ts8jdxp-u s :pl: g( 0+qityine the work done 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 particle acts i- nny81nko- kfn 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 maf dlp-/w ;)reoss 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,b /p: +ssbozi(32cwb n 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 requiredq,n(r aq r)fk5 to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 105k1 i:c9jqns/7 cgok7unt.i.n i m/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string ex7+w5j/g ejc y1qn15 hnjhr*2bpf oht1erts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the b1q1gb725ot wf *jhph1+rynj/ n ch5jeow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s g/l o xdp:)b/fhj9085xzue sj wlove backward 25 cm when the/jb/uledp :xz5s x0 f wh8j9o) ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is 3(;say8ci0wbyk 0-u hbn(vth increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the ba t(hk( vn8y;sb3y u0-wich0driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skw74r5iihkg;9zc/ a j vid mark 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 carj9;v/ka5 w7hg icr4iz 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 rvquf2m.vc20 :-ep 06gf j v5v(vhbjo pitched at By the time it reaches the plate, it may have slocjorf2m.qv( -0g ph v :2 jebvvfu6v50wed 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 ro,5.w id/ ) lawa(bnrvmck go if thrown straight up by someone who does 80.0 J of work on it? Negleb )a d, i/(n.rvwm5awlct air resistance.    m

  A 285-kg load is lifted 22.0 m vertically kvrz2s8u dc 5 +xdp8h8with an acceleration by a single cablpv ks8cx5hd 2+88drz ue. Determine
(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 44uocn10ete1x2 lxn y6lw aeo.6 58km m-0N/m How much must this spring be s8u 06me1-yl xoclwoet m1a 25x6kne. ntretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch t1 xon,*w-v wyt i3a2sjo another 1.2 m higher. What is the change in potenswiv 1 x- ,2jonta3wy*tial energy?    J

  By how much does the gravitational potential ct0 -p7nua+/e ,9t0elds ecdl energy of a 64-kg pole vaulter change if his center of mas0a/d-, c7es0pl + tent9eu lcds rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfacepnec akoqw/(z/935 or has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the s 5aqo ow/ 9n/(eczpkr3pring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the gr.llfui:mw,(azk:t2 znfwv, + ound so it is 2.20 m above the ground. What is the potential energy of the book relative t2+ia,l wfkm:u (zw.ntz: ,vlfo
(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 to the top of kpvl mki a5w.c-+c f,6a 3300-m peak. kpl+.,ak-ic6v5cw fm
(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 vertical xnk6nqttw-38mlz:a7 e t(r4u7 r.avtly next to a ruler. The end of the spring iaa7n4zm(q-re8 3ltttu xr.t67 nv k :ws 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 will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzmfir4 x;h*w3 dan, 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 sif4dh * rw;3mxwing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35bpb/ ouh5bfzj(o+k l8ve4 5hf;6r 5yo.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 a frictionlessqoq0jo 1n10d wrse6+r 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 into gravi wlvqb+ +iwf5t.9us)0a/oa rgtational potential energy without the aid of a pole. With what minimum speesgr. w tbow)f90 +q+5iv/aauld 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 upward from the top ofs)vdh , cw8 kn0yq-al6 a platform with-dw0ay l86ch)k,snq v a speed 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 n+ltze ,*fyd ci (q4za3 cq8 myy(k5m.constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwa e.(nt3 qc zcka*58m4+qiyf,ld y mz(yrd 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 Fwfy2q 4kbm6; 03mavlmhe9 lf. ig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r),l 9lwa23q .kfm 0e4myv;m6fh b from what minimum height h must it be released?    r

A block of mass m is attachjet 77h,sdqk)ed to the end of a spring (spring stiffness constant k), jd ehtqs7k,7 )Fig. 6–40. The block 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 bridge. axj57k6vdocw:)qgn, 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 cord, assumingj ,kcdvxo6n:7 wa)q5 g Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown nql x1. ;vsrnlnvche7-vw/5 : in Fig. 6–41 is dragged up to point 1 where it is released/7 lv1nsxrn.n -:vv; cqew 5hl 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 m/s at aw zntv/+a+q9q i j6sq7n 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 sp k)/+ o;:yhcxz. tz yuc+1rev+dz2 odwring to be placed at the bottom of an elevator shaft. If the elevc doue+otv) zw.hr+z ; dy2:kczx/1+ yator 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 mass of the elevator and passengers.

  A cyclist intends to qbm)8 p*tld6i osh tm+ *3m;dfcycle 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 tr8jcw 17 scsxw8od967jpby c8q aveling 95km/h in opposite directions, collide head-on and come to rest. How mu s8 s 7cqdc xp8y9wcbw17j8oj6ch 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 andlsn xeitqx yu911m njqgw e8. i.,4s); reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction wnxtmqlsw8)e4; n1j 9 sq e1ix.yigu,.as generated in this process?    J

  A ski starts from rest and slides downc,*ihjit - et6 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 dropz ueu, 2 zldn.rz0 oj..:ng3zhped 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 r*ycv4h+ 8hzrit bounces back to a height of 1.5 mr* 8z+4hvhc yr.
(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 pullq k 7gaph71zpbk;2 x(ded across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictib 1h pkg p2(7k7dqx;zaon is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes p/ yucg/k:*jk d;+r+ ux3x pkzloint 1 with a speed of If the average force of friction is uz / c*3ujr+gypk;lx k/+xdk :equal to one-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 a st e/2zwi(.cslo0*bocn eady 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 attacrg2l912o *d16ek mwy,ae psg8 9qjo wkhed to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the blockma9wkpsrj1,o 6ke9q 2*y wo8deg 2gl1–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 kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizonta l-7sj.d ajq(gl 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 rgdqja- .(sl j7eleased from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for99 otjou-u;c60.rtw2n xrw)xmte6sv the 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 been in9o2u6 6.rtruexwtv njt- wo; x0m9sc) 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 piano tsvn6 xj,iqb6jt+gp 9/ o a sixth-story windowij6/nvx,g+bjt p9q s6 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the avefd/pj*c)ca8p rn+a2 h9iuwr44wlt 9 h rage force exerted on the car due to friction8hhn9a4*+p4iad 2j)/l9uw pc wfrrt c and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4dbx9p): x gw+5/ hg77yoq kxhb s. What is the average powe +9bhhxkd7 xp/gwg)7oy qxb:5 r delivered by the engine?$\approx$    hp

  (a) Show that one British horsepoweraf 84uo w.*zuieakfv/x of n(;gk5t htf 2r58:$ \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 the form of “kilowatt-hours.” z 4c0*-wd701p cenbzc gd .snt
(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 from to 65km/h in/ 2pocj8gm2fh;k 2vj8antt;o,5 qdar about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep tj5dvp8aomkj ; 2;fc r n8 a/oq2tth2g,he car traveling at a constant 75km/h.    hp

  How much work can a 3.0-wp z;( 0nxnas8hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a vfax or a geu;640urhl; +xr,reel1 )dm q-55k7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was develo r0;4e 5akeg; erq1x5fh,m)-vldoa6x +lru ruped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute thr ;x ,yrs8zaqmau;- n25vicre-ough a height of 3.60 m. What output sz iu85n 2ya;r;q,rea vx-mc -rating (watts) should the pump motor have?    W

  During a workout, the football players at n* a ;lcwen;.nState U. ran up the stadium stairs in 66 s. The stairsw ;.enclna*;n are 140 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 cycl ;d4oey p:qm;)py5 qd;3oaa: hqm pcu6ist 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 maximvh1gln;vq 1r h qi4kf3v 9(ca8);s lawum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces aw;94lck n)sqravh1hgqf l(;v av3 1i8dd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be wjuhf01hum7pg (19j iable to drag a 310-kg box along a level floor at a speed of 1.2m/s if(pi0g1 h1uhjumj 9f w7 the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7szi 8 )wxbda,/.0 $^{\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) bumpers” that -9/zac8dc kklare designed to compress and rebound elastically without any physical z9lccda-8 / kkdamage 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 shelf is 10.0 cm off the ground, -xf-pudzv i b6(s39bxand 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 shelf holds 25 books, how much work is required d3u(p b69 b i--fsxxzvto 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 1936 Olympics showsofr ; h0gw6s8y that his center of mass rose 1.1 m from launch point to the tof6 o8rs wg0hy;p of the arc. What 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 frictio sxo1p .6ud .7 -l6qeu pif;l+xcp4furn along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of rad1 ci.4uplu+o7 x- q xl6p.sfrue6pf; dius 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 jumpa 8)20ojjlk0twgzup 51fr2 ywing from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg anj2 )p0 gra5wzfutj28wyl ok10 d 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 fi 44s4nqm4alhk xed (Fig. 6–4k4 4mhq4s4nla 3).
(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. 4rm6hrwena b8413fbtThe climb is made in 5.0 h wrh4b nm b4t38 e16rafstarting at an elevation 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 9p+m c6 bckn*h:j/s7 rab3xd bnb;3v2x20-kg elevator is 28 m 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 in California claims that its lifts c2gp xxct/r; m*an move 47,000 people per/2 cxp;gt x*mr hour. If 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 and f ,-qo*6dkd yycalls vertically 81 m before strikqoy *, kdcdy-6ing the turbine blades. 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 withqry3;rcciag8u 3t9d/ 6,xkn t a circular vertical loop (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 also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the kxtq i8c;3 d ct 6/aruy93rgn,loop or how fast you go through it.    mg

  (a) If the human body could c*fqbtd / uk(eek/c s4-d2x y;qonvert a candy bar directly into work, how high could an 82-kg man climb a ladder k 2t(4 dkcfyb-xs;qdq/e*/ueif 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 firecb j l b+*js9loc5,c,l m5jgrfl1f9 :rd at an 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 sprt/ujtci r 1 ajjz9.ls/go9 73bing inside the scale compresses 0.60 mm, and it tells you your weight ig/r7t c9.9b 1ltosu za jjij3/s 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 swings out over 9ag8 tru5+ gyga lake (Fig. 6–45). He releases the ragt ry58g+g9 uope 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 distanc,3sx.ub8 zh ca ,)ljvce of 5.0 m in 9.0 s. What z)scl h3uxab ,c8,v.jminimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pbq9xcguu/z:m0 7l5dh2hvbi * umped by reversible turbine pumps from a low to a high reservoir. To store the energy provgx5*qh:mbhzlu0ic bu2 d 79/duced 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 stif;e6obc0zm .vy a x)lr3fness constant k is cut in half. What is the spring stiffness con .0l 6;orbxz)c myva3estant for each of the two resulting springs?   k

  A 6.0-kg block is pushek-oxg b c2u2ez-3ct2md 8.0 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 from 35km/h to 55km/h in 3.2 a ik,hxx5rxf*11as5ns, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays*a 115f ,x hianxrxks5 the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walk g2nc:7evq k0d+w7q fxs on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when ckn gq7f 0ewd7qx+:v2 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 vertically upward a distanr9 ,o/jovds a( 8kkpbpkn5 4h3 ckt(3qce of 500 m, what was its velocitqp8a t34jk5k hon9rcov ,b/( k3dp( ksy 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 watmpnp hzg td1-d:38vn2er 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 is its maximum pow1n gpd 8-vn:t23 dmphzer output?    W
(b) What is the speed of the water as it hits the wheel?    m/s