In what ways is the word “work” as used in everyday language t8.4 tuimoi6gghe same as that defined in4itmgiu.68 g o physics? In what ways is it different? Give examples of both.

Can a centripetal fot yqpd 598u8ump)dg ;cul m21zrce ever do work on an object? Explain.

Can the normal force on a olpugq d)hq)6;fr,,::r h9vzxtvw) en object ever do work? Explain.

A woman swimming upstream is not moving with res j*imzzjxp ks15 mu40+pect to the shore. Is she doing any work? If she stops swimmi0u4z s j*ki+m mzxj15png and merely floats, is work done on her?

Is the work done by kinen-nt70b mp9axzm-, r5df; bwk tic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tabl9fn-,xtnw kz0 ;m- 7abrbp5md ecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doi78pd x)-qb+ en 8otawbng no wore-t dnw8a8bqp o7+)xb k?

You have two springs that7ia:uu 5.f0pu,yg9y)e vg owy r +vf*h are identical except that spring l is stiffer than spriy yuy) :vg r.7+ e9fpohv a5*igu,wf0ung 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 nwzv 338k9tn4+kqh av 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 baw4k33+vk9 h nnt qv8zy 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 much does your grav,wecpai9 zt5er6 f8sxv ;2h h6itational potential energy change when you jump as high as you;,6zate59 swip r2v8xhh c fe6 can?

In Fig. 6–31, water ballogv m jh(88,h41 m9q.qjgsj8otnbp +h qons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air roqbq89.h g 48mphv+hj( 8sgjnqt ,jm1 esistance.

A pendulum is launched from a point that is a height ;0*pyjsgqvq(j.iie d9 (+ p azh above its lowest point in vqeq0y (9a giid(j js*.p;pz+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 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 yo9e5+ usu :a xeg*zdp1ziqim5;u compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the laieqzi *m5s zd 19u:ge+x5;uapw of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inrffk *nf h -t2.+vrdx(structor 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 pushin*hdtk2rfvf(.f- r+n xg it. Why?

What happens to the gravitational potential energy w3jmqfegy/lg8 s7kd1wg5hn- aue0 l95 hen water at the top of a wateg 5hq71 nf 3-g ea/deyjsmk58lgw 0ul9rfall falls to the pool below?

Describe the energy transformations when a child hops ar7. 0ecknlugn glw1;v6h5 +/kgw e6xg pound on a pogo stick.

Describe the energy trans3ja-cs f3 roalnsi1)g-q b -/mformations that take place when a skier starts skiing down a hill, butssca- -bj gna-if1r3om3 / lq) after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts frr0o6 15 xt:bbzm vgh*wom rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hwtzh0v: g5 ro1 bm*b6xill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to 0x1m9lga4 kxm+vo i+o step over a fallen log in their path rather than stepping on top and jumping do1x+ +vo lmxamo 40igk9wn on the other side. Explain.

Two identical arrows, one with twice the speed of the othe b41bus tub,:mlwo;c 2r, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrowss2 cu14wb; bou,lb m:t, 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, (a) ignia+fsc/ ks b-e5(x;t/ltdt* woring friction, and (b) takd-/btal5ssf;x(t tei * + cw/king friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gr:5 jl2a :mqw .v:irsdgeater than its original height? Explain.v.idqj2rl w::g sam5:

Suppose you lift a suitcase from the floq ybo.4v-,hgrl s+ -bjor to 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 olgrqvb-.h y4+sjo , -bf the suitcase?

Repeat Question 22 for qy8e7t9 zy *0ojz89wq xdfw ;zthe power needed rather than the work.

Why is it easier to climb a mountw8.m0o r -hywqyas 41zain via a zigzag trail than to climb straight u1wh4yao 8z-y.0 wqsrmp?

Recall from Chapter 4, Example 4–14, that you ca(zdm a)e12h9sstfg8xb+ z2sd n use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, xe)b2zgsh 8s9d zam(t 2df1s+how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fa*uf h*3 msxh2ulls 2.80**h32 muf xuhs m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0wxi+7ma8 4a4hj pt(px m high. How much work is required?x i78wap (4+matx4j ph    J

  A 1300-N crate rests on the floor. How much work is rd 4y3j+, kylc6ybd3f vequired to move it at constant speed (a) 4.0 m 6d y4 y3f3,bv lcky+djalong the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movee*y91wbqs )nh5 13ch 9svgnr jrs do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effectivejs1nb9)51w9g 3nc yshv*r eqh coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceler+5-.scxx z+ ik9 q,bkosocu j2ated by a force across a floor at a rate of for 7.0 s. Find the net work done on the bo soz 9jc +-sk.2uioxx5c +kq,bx.   J

  Eight books, each 4.3 cm thick with ma7v37m pklph t(5d u:uass 1.7 kg, lie flat on a table. How much work is required to stack tpv3 uha7 :ptl5umk(7dhem one on top of another?    J

A lever such as that shown ind ,o glxk(1snm(bx/i w (u/mm7 Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output forco7/d xw(/,smkibu n ( (1lmmgxe, $F_{\mathrm{O}}$, 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 bydlv(gvj/lx oal/0: 9 v/ *b 1c4anbfde a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefdal/cjoal /0f le/gvx(:bb9v*d 41 vnficient 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 jwwm x9nw i9xedt9*dzcb;+,uq*6f f9 M an acceleration of 0.10 g upward.f9 ,x6w9mun9dzw*xj;c9 fe + *bqtdw i    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 an,)r7br+ v-ysyqa3 c4 5iw wtfdd 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 axg9lsj 9 (3)8jp lpjvknis, varies as shown in Fig. 6–37. Determine the work done n 8( 39pl)kjsljg 9jpvby 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 in thbwuv3tevz- k0rt4nu+i p22 tsp,b 5+ae $+x$ 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 7d)ow g464eytitde6e :p9x kb0u2c;bzbz xa4molecule, 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, by whatpj khte7zap 1)..v9q p 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 awbeg/ n7 e0;osl r fmlw9opjz;o21+ y8n 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 trahyvo6,.o14f n-f amek veling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force hx7dhe n f.oebq2.rc m +ed7v(1/w:txns-2itof 110 N on the arrow over a distance of 78 cm. What is th.s -.oec2irxt+mtxq1h d7en :bfvd/ e hn27 w(e speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a8 *d5.sa /ijqxa0dojs fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the 0oqx s5.aji /s*d8ajdball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum braki*i3j)3 qyu+f 1m5jc+bw a4jnb )uo xhang distancwnbxhi+ *) m34 qju5 fo)auj3+j1cayb e be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators me3v vs83zw7wvi12 w. mqujj fr-asure a car’s skid 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 car when the driver slammed on (and locked) the f1jw v3u-3m.wjviw8vqrsz 72 brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By t7 t33my c+upa0ojmx 2ghe time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a7x30 mgt p+3uyajmo2c 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 thr1k/ qjtf( w0kcown straight up by someone who does 80.0 J of work on it? Neglect airj0w1kfcqt( /k resistance.    m

  A 285-kg load is lifted 22.0 m vertically with q uxk*la6efmh5(x l8r xv8j *.an acceleration by a single cab6*qfulm xhv8(kl8. ja re*x 5xle. 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 sprinb /m6 -1pvduzdg stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potendz1m- bdv6u /ptial energy?    m

  A 7.0-kg monkey swings from one branch to anotherp pkeutc 7+i -et+4 d7ap0jnj( 1.2 m higher. What is the change inj7+e(4c0atipuj-n 7tdpp k+e potential energy?    J

  By how much does the gravitational potentiald7ol)mgnpd:k )eie6 s2y) 1it iuv ;3b energy of a 64-kg pole vaulter change if his center of mass ris;6:b 2i7miled g opv)3ket i)dysu) 1nes about 4.0 m during the jump?    J

  A 1200-kg car rolling on a 7:d xn;) nyqao3jif1yhorizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring andyxq nj7a;d n3o1y:i) f is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person le liypljh m:nd, vfyfs98312*ifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative9lj8 l3yf,ni yms ed12hfv* p: 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 to the toa( y;:ogmvi/p4knof;uy)n 4e p of a 3300-m peak. 4n:na)/kev fomgyp;ui;(4oy
(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 verticallyn8y2* cl vzz6y lb:yc5 next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg masvzc8ynl:5 ybyc *l2z6s is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine hac*;tj-ekce)4b 7;bapcq g o;f a rcc;+nging ;qcgkfct+e4jb ;oc* 7; a;bcaecp-r) 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 ap,;lp 2;mvnad frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a smr.lf p.j*gvbpf(e2 * x2utl n(.nqd 7hove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational p ibqj;qdumz :pn2/f2( otential energy without the aid of a pole. With what minimqm und2 p:;/q(jib fz2um 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 js,( l q,)fx kl(pjjka;umps vertically upward from the top of a platform with a speed of 5.0 m/s)l aksj pfx((ljkq ,,;. ($\alpha)$ 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 is 950N/1n(ig;;,us8lz 3q hj fgb5crf-z1 vytm is attached to a table and is compressed down 0.150 m. (a) What upwaf18( 1 3yhjtqgbvlg;5r;szicf-nuz, rd 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 loof7ikm x;0 ds2zb zs n5-s5l,unped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h musts zkf5-mu snxd ,b2z7l5;ni 0s it be released?    r

A block of mass m is attached to the end otpt2 g);7egx9/so 2jmste5ol faq8(mf a spring (spring stiffness constant k),fx7tes)9l2( 8ta/ge 5m2o;qg tp somj 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. She is tied to a bungee cord whofl8sclc a8s8j n1v(u g 8hkc;3se unstretched length is 12 mf3 ng8l 1lscv;8j8 uk8s(chac , and falls a total of 31 m. (a) Calculate the spring 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 shown in Fig. 6–41 is dragged up to point 1 wherhh+e 2+e t 64u6bo2m:ylahx0hp2 ensk e it is released from rest. Assuming no friction, calculate t hnpbe2tkxeho 2uh s6ym++la26 h40e :he speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 123k c8:bozyr5 v m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be pr 6 d;qqxf7)c6/ppqn , txnec,,igqv*laced at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above t c xqg,q*)e7dcqp xtn pf6iqv ;r6,n/,he 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 cycle i2jum6 (yu*tow;i * j.tfm -jzup 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 7: bmr70-j lyzi650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How murij:z mb0- 7ylch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wi o;oaqg(u84z92 p xs8kfi u;nqdn-8dbth a speed of 2.2m/s How much thermal energy due to friction waf8 xzn8-qaub;i nkug8sqd (4;d9o2op s generated in this process?    J

  A ski starts from resthefsk2ki g0f: -sg 9j pr34jr3 and slides 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/ 3 b wifnzxhpag96r34 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 bounces back to cp1duh 4tenv ;p9q a88a height of 1.5 m. vnhtpuqd8 ;4ep c1 a98
(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 ac;-m:/ xubpmqaross 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 friction is 0.30. What is the f-uq pm:a x;mb/inal speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a si)d8:: bonh:ev .7fruu d jwe,peed of If the average force of friction is equal:ddou.h:7vn e,:e8)j b wfrui 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 0dy)pyf vivsx+i,s1+ sk14xvx 8 k bd(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 horizontaxjb l-j:jgs-4 t* -x;l+kzqe xl spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping ande; tq*-x: z-k-lj+j4bjl xgxs turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly l5f/vig 2wls4:9g dunattached 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 compresgnv5/digusf lw2 l 4:9ses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glv)j)ydk 92xxks j19vm 2 l8ltqider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventu xxd k l t)j)q9m22s1klvvy8j9ally landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story(*:qq gu fj)pv window 16.0 m abovf:) vpjgqu(q *e?    s

  If a car generates 18 hp when traveliyxw+65m,go ahv p4:wx ng at a steady 88km/h what must be the average force exerted on the car due to frictp v46+:may ,gw5who xxion and air resistance?    N

  A 1400-kg sports car accelerates from rest gv.pp bi/e5y( l6 qkz gf.ri9s *4dp3lto 95km/h in 7.4 s. What is the averagev/b9e(prqyf56pzlkgsp3l ..i*d 4i g power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepowd /(dm1z nahw(er$ \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 7a (k;ha wgs)zof “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 xzc61mras;1 0f8cb/c k-xd h adown from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constarcax0 m6z1;c /hkcf 8b-1das xnt 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.s(zz av:qmp1.zday;. 0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/sq 0z -(v:qy)pcohsc7b If this motion takes 1.5 s, what average power was dq -:s(cyoczqbhv p) 07eveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What ool6h8p :bo4f-+iatvt utput rating (watts) should the pump motor b- 8aptvih6o: 4to lf+have?    W

  During a workout, the football players at State U. ran up the stadium stai208t wx7j52vsmi qdw jrs in 66 s.ts0d vww2 87xj im5qj2 The stairs 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 cyclist cp6 o9o trb*5msal4 ik,limb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How ste5 / em;ony9 14j-snlnza ivnb6ep a hill can it climb at a constant speed of 75kmnjsn;65 ez419l -myabi /nnvo/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be cbfponc,h +8+.1fy kz able to drag a 310-kg box along a level floor at acyc 8pf,1 znhofkb+ +. speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dowx)ncf. t;bzwmzz:h wbb7s.+4n a 7.0 $^{\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” ti. k-f2 u7x j4n7uyabd:p h6eohat are designed to compress and rebound elastically without any physical damage at speeds below 8edpk ju2.y6 ui74 - fbha7o:xnkm/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,w s a077vnf:bbhdqh:, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how muw70h vb:dnsf,b:h7 aq ch 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 (g +rka556tnrxt.9 glwraj6c: al, 0 hnFig. 6–42) in the 1936 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 travelinltg 5r60j6nx halwk+ar r:5.,ca ntg9g at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the dcnhycphvf7 . i:fq :n:+jz0 /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 raq cz hcf0jf.p :v7/ih:n+: ynddius 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 without his ,/y)scz6u:v jw:rf m xparachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but)zw m 6jvs/c,f: rx:uy 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 horizo)emlfb 2lg - 0)zfooh*ntal cord of length L whose other end is fixed (Fig. 6–b2fl-o)o*z hf l e0mg)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 370oh 9;byy-1w5 hn* +kfswrbq8sis * /os0-m-high mountain. The climb is made in 5.0 h starting at an eleva o1*i*h8h ysf;sksbs /-+59rwbqwny otion 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 ,rxp w2 mc df )tp,ym7lnm880labove 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 Californiawq4am2 o,ama at fbs,7eby7:zu186zw claims that its lifts can move 47,000 people per h,zam2a:7m azs8ty76u,q4bf oa1 e wwbour. 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 falls vertically 81 m beforeyg 0abaztq 6le:4oyx n-05r(j striking the turbine blades. Calcu0gezx (l5:q ybay-t 4j0raon6late
(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 (w5:o1sj kc44t4yd xf1izk29v (p oihrFig. 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 nexv 4rwzky4f:dkjho i9 pti41 c251s(oeded, 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 in toz z4 *aqgvri8oq/1 -y:+yrbto work, how high could an 82-kg man climb a ladder ifr+ q q i 8*tyya:bz1-or4z/ogv 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 angle of 45.e4mgy5s* b .ua0$^{\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 scalz1 fqgtcow,cs 3/w /lt;;: wml(wa n5je compresses 0.60 mm, and it tells you your weight at :fz(5j wcs 3n ow/l;1/m;tc,lwwgq 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 swings out over a lake (Figp7/be2tn q8zn . 6–45). He releases the rope when his p/n87qze bn2tvelocity 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 5.0 m in 96s6w) zs6ywn- vozr0-t: egu u.0 s. What minimum power outputuenw6os t :s6z0 ywz-6g)u-rv was used to accomplish this feat?    W

  Some electric-power companies use wate,h c db3vnai,2r to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.ncia,3 dbhv,20 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 is /5 k (u8 wn:bz epb5qo .;iftg-xgyvl3the spring stiffxl3;:k5ni/zgf 8 t gb b.quyo( 5ev-wpness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37hnxj 5s(erg y5 1v+ns, $^{\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 n mi873sg2.h/hv rcqb accelerate from 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, and neglect fricti/2s 7br8hmn. vhgiq3c onal losses.    s

  In a common test for cardiac function :j l*ou;zjgwey6fdipr3:z. -(the “stress test”), the patient walks on an inclined treadmilul:3 z*j.wi d jfe;zgryp6:-o l (Fig. 6–46). 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 verticaosg s1 /gbo4o yg)bia)k .wi4)lly upward a distance of 500 m, what was its velocity when it left the vo.o bks /siibwg414)g) g o)yoalcano? $\approx$    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 waterj..9.t sxvz vw wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electri.xz9j s vv.tw.city output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s