In what ways is the word “work” as used in everyday language the same as t(lg tq2d9dv/w hat defined in physics? In what ways is it different? Give examtgdw92qd (/lvples of both.

Can a centripetal force ever do work on an o.pp0i-lqxeo min9 3;u 9h7v onbject? Explain.

Can the normal force on an object ever do work? Exp-v;tt iq+ )bxxh-ve;blain.

A woman swimming upstream is not moving with respect to the shore. Is she dokb3sosbh5 qtp: 4z-cz;*kze.ing any3 pb scz ;-b5:*etks4zhkz. qo work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Considegl7v kz:.n+- n n.h3yv6w00ht1slnii/ kaesmr what happens to the dishes when you pull a tablecloth outysaln sg/wnvhv n601i 3k0it+ m:-e. .7hnkzl from under them.]

Why is it tiring to push hard against a solid wall t5c o++ek2fui even though you are doing no workf2t +uo e5kci+?

You have two springs that are identical except that spring l is stifvuuwflf:fck- *b9 cgz g0 f o/i;/gd-1my/;hlfer than sprinbfg gh v fm/1fkcyo0;-;l 9z lud -uc/w*/i:gfg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that ys nw6u/cy *,r 1m.ggmis free to slide on a frictionless surface (Fig.6-30). The block 1.wn/rm*gmy ug6cy,sstarts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change 2/:ex6 v;4 qmm8axpl 3xmpopo when you jump ;2: pxx6/p8amp3vxlomm e oq4as high as you can?

In Fig. 6–31, water balloo:pzyc5)f qadhh 3-y/ wns are tossed from the roof of a building, all with the same speed but with different launch angles. Which oh)-5dywz/3 qfh:y cap ne has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a nnope2s3yz 1s 4yf:3g zev.) hpoint 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 along the trajectory. Which launch will cause it to p eo ye4gvhz13.zfns y)sn:23swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tuw+4k j.0hzayu1/ pn-edi vp .e20d phable. If you compress the spring by pressing down with yourejyadk1h2 wv dp.e+0p ziuhu.pn 4/- 0 hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hungkm8 k); t4-/gckhdck * bekv9v from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands aga;84v et-*gkmchkkk /kd9bcv) inst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational pote: 5ozzo 0zc ,nj/ 4ns;e9zwgfkntial energy when water at the top of a waterfall falls to the pool oz5,90of;g4nnzew z:sk j/ czbelow?

Describe the energy transformazdr91/id -eqw tions when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiin1ocqst*hip (2u:q9l+j kq t/cg down a hill, but after a time is brought to rest by striking a s l* k(stch1 2otcu+q9piqqj/:nowdrift.

A child on a sled (total mass j v zvk9r+opo08yj7w(m) starts from rest at the top of a hill of height h and slides down. Does the velocpjw0+ozvkvr(9yo 8 7 jity 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 ozgsx26e q8ompr a7iq+x(0s7nver a fallen log in their path rather than stepping on top and jumping down on the other side. Exo( qeq+8xg asxr6mip 70zsn7 2plain.

Two identical arrows, one with twice the speed of the other, are fired into t eh0tp(mf,gjpg7 59sli*z4sa bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Expl fp(,smg0jh gte*z79lpi45t sain.

Analyze the motion of a simple swinging pendulum in terms of en9mp9j/zs wo 19f dgwhkj3zb:3ergy, (a) ignoring friction, and (b) taking friction into account. Explafjp m3k/9b1: s939zdhozw j gwin why a grandfather clock has to be wound up.

When a “superball” isw 3-cjt dgf5 rp/kc52v dropped, can it rebound to a height greater than its original heiv2ckjp5cwg 3d-f5r t/ght? Explain.

Suppose you lift a suitcase from thv8+sd s5f 3xeje floor 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 3sdvs5fxe8 j+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 power needed rakus ,fvob9p 27 bc*sc1ib0b2mther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strk24q9 t7bfqh4 ydwyq ep6r(;iaight up4wi9tpqh ;ebk2fqry46 q7d(y ?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rp2k)fjsh2nsr n9 k 5*2k1gpk sopes to decrease the force needed to raise a heavy load (rk s sknkg hn 21*22jps)fpk95see Fig. 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 gxo,1,h5hae+o jh-+pj 8ufmnwxe0 3 ryravitational force when a 265-kg pile driver falls 2.8o+hju n 5h, fyex,3re0op8-w a mh1+xj0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work :sy :x9dvg + bz 8urdy2qvy+5qis required?+ 2q98v yvdsdqg: 5zybxyr+:u    J

  A 1300-N crate rests on the floor. How much work iszv7pcw m0vi(lhpu55w p.ut- / required to move it at constant speed (a) 4hz0u/7 .l-5cmp5p pvwv i (wut.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) ye0fvor,wa 1 4pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of va f14y0e,ow rfriction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rat.8/dqskwm,s puxdbx +vt.m:h 2zvb*y eb*4 9se of for 7.0 s. Find the net work done on the zv.d m. *k,vmu : py8/b 4sehb9x 2qs+xtd*sbwbox.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How m)y ;;ju i22he9fll:tmkvnxx jt 8zh6/uch work is required to stack them one on toyj 8hzxjtekf:/n ;h2i9xt)v l ;2l um6p of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff2 kz v6;bi.rc uevqy(, objects we might not otherwise be arbv;uvc .ik qy62e( ,zble 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 accelergrlbmgme20b whn9+ w29 k 2cl:ating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectih cw emkb9+mrb22 lg2nl0wg:9ve 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 helicoptea+beyv8* x q 8z ntg( -lpgeue)lzedz+ 9ks226r of mass M an acceleration of 0.10 g upvu)xp q26e-bgzd 2(s e+*an8+lzl ez tek9y8 gward.    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 tvngf ;np 6/:9cu5x i*ll xgu7yhe distance 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, acti)w) +(+imcgn. 9nu gnjl o:t0x ykq-iing along the x axis, varies as shown in Fig. 6–37. Determine the work do .ylgn)0nqcju+ -t i:i+o g(kn9mwix)ne 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 parss fckwzf +(17(ags j6ticle 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 molhr9hgzg l;b4e8tj3x8i/ rfh/, dp0o zecule, 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 whatlo q;*v8l 0 ifm*iycx6 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 requr(o mk6 7*/9wsaxbfv 4o eu0vrired 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 t8rwg;+u wxious ,*v,no stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string :.xunmx g,x/wr6n:i3gkvn 4bexerts an average force of 110 N ox vkw,/ n rbmgnu6: i:xx34g.nn 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 m)timo s- :kg/voves a fielder’s glove backward 25 cm when the ball is caught. What was the avergksi: o -vtm/)age force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%xaztcggwki2 ),1 q i*(uf*9: q.a ifjh, by what factor will its minimum brakingx2 zaih g9*ig(wuck1jffqt a.iq: )*, distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,,i2qcvkx +h2h o,4r zd investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was hr,chxoqz 2k24+ vi, destimated 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 0bme(c+ac j;p7.25 kg is pitched at By the time it reaches the plate, it may have slowed by 1+cmcb7e j( pa;0%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who do.v l4f q u3w,(n1-zqyfx,uma des 80.0 J ndf,f-4y wux1l qqva 3.mu,(zof work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vermqwi-e*39fsu4vpr-r 2 *f e92b6bmm y) ocnbltically with an acceleration by a single cable. Determineb23-ew4bv*nm9sy *lp ubrrm9-fefimc 26o q )
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/-gs.thw9i 7 ld/; h.mobnuy+im How much must this spring be stretched to store 25 J of p-dt;ilhb9ongh+ i..u msw7y/otential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What isx nn8 *onkf,e( the chano8f,nexn(k n *ge in potential energy?    J

  By how much does the gravitational potential energy of a 66cljf(-q af ,u4-kg pole vaulter change if his center of mass rises about 4.0 m during the juf fq,-la(6cjump?    J

  A 1200-kg car rolling on a horizontal surface has speed -y5 3uy8q z 9eu9i7xuy,srwiiv = 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 spring stiffness c- q3y7uu9wzxi5yy9si 8eui, ronstant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m r+b ;mhbq;o x5above the ground. What is the potential enq+;mbh bo5rx ;ergy 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 elevaogd h fz12l/:ktion of 1600 m and climbs to the top of a 3300-m pe/d2hg okf1l:zak.
(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 h,wn vx( jht.h;ov4 o/langs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of thh.xwjn,(ovhv;o/ 4l te spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is r-gnfehu)17 sc unning at top speed (5.3m/s) and grabs a vine hang e f1gsc)h-7uning vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictif- n6 ua:l8r)(pv sb /iyokh.konless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a e66 z (zhj)eqepg.e) 1mxbl:f- uk kr0frictionless 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 gr0wto:. nyi fth aotw; q- mlx/.8k8z-zavitational potential energy without the aid of a pole. yfzz.n w-q: tml8t hka-oti8w; 0./x oWith 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 upward fxr;;yxso;izwk )+j+k rom the top of a platform with a speed of 5.0 m/i ;kr+sz ) ;+xjkowy;xs. ($\alpha)$ 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 m;wlyt)qgx-f 1nkt a3dp4+m s 8ass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0y8;43pafm s+gtx dtn)qwk - 1l.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 ly5,7ry nk zto. kp +u:kol1i1ysb.1bfriction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circnlu:5+ 7p.1.ts1iyly 1 bokr o,kkzb yle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end onu mj68wgy*n) f a spring (spring stiffness constant k), Fig. 6–40. The block is givemwg86u)*nyn j n 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 l5)j.lm95wnzfo *o th 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, ass o59.lztl) jwmnof 5*huming 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)o *qnoj9y8b dx p-.su. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calc*p n o 9db.yx-qsuo)8julate 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 ah gpt,7du/4ocn angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the ig 1r7bzv1x3h.uk.a) ezh7 v ebottom 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 constan1 ha73xrzz 7hb1)u vvige.ke. t 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 cyc o0s uy5g;a prv h. wzdy1zd2495dk;: a(sgcrxle 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 travbi4g/ue k6(m:s;dc (so7gtk ueling 95km/h in opposite directions, collide head-on and come toubm4s6ge o7sdk; /( (kci:utg rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m k;:h5r zv,-pir8 yb3qy bgm 1mhigh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proces- 8p;, ik 3:1vmbhryzgq yrb5ms?    J

  A ski starts from rest and slides gznq;8ypy7 eg (h6 )kndown 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 13.0 m above the g) 7okr-dle6v: 0vto ruround.
(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, a:jr3/bdwj f1aq kz /w;nd it bounces back to a height of 1.5 m.w/b : w;jqrd3ka1z/fj
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constanp;+6xn /d1cg;ey xjmdt horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction +nc16 m;xy/xdgd jpe;is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster d.5h dklms)2z1.ga9judpza : in Fig. 6–41 passes point 1 with a speed of If the average force of frd.:pl. uz2gmj)9 ddaas15 hzkiction is 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 stea slzua da)p4 ozv7g-gt/g/)m 6dy 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 spr cz 41 /jrrjk .j.l9)ldgray;ting (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the blol/.gkz9a) c rty;rj j4rd.j 1lck and the table?   

  A 280-g wood block is firmly attached to6 jqbl 7 kuczt4)nm8o; a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equ)o;ju4ntq cm7lkb8 6zilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 9804/l6* pvh qy0 bre+kbn kg including pilot) thatl*hb/ krynvp +ebq064 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 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-storu80s/ea* ga7dn uia-5hlja61w , lcy ey window 16.0 m abovels/g-ej cu5e86h aya0,*d1wnai a7ul?    s

  If a car generates 18 hp when traveling at a ;gu jr4*zqe jrj6 i4xb vmc4x-:h(w;bsteady 88km/h what must be the average force exerted on the car due to friction and air resistance? ;u-x4rh ij(bq gv*6bem;z4xw4j:cr j    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whayx a ,8;-jwod1dsa9.4cchcqy t is the averas,q dc49 cox1jd8.y haa;-ywc ge power delivered by the engine?$\approx$    hp

  (a) Show that one Brgk5ia0; qqpxy* oe-m,itish horsepower$ \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-r d3z ub.7elti5e (lg: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 dow+ysz w7q2 b 8o/p(y iazkq27izn from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is need qzy/i + ( sk7qpowiay8b7z22zed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp o y:/t tnnqc a*5iv -*i3 vhc1o61sfjcmotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest uk6-as v/ur8sm et,gg q200prto 14m/s If this motion takes 1.5 s, what aveksgur r/mg2qtpva-80su0 6 ,erage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of wat)r+i 7ie6sll per per minute through a height of 3.60 m. What output rating (watts) s pl6 i7r+sle)ihould the pump motor have?    W

  During a workout, the football players at State Uv f11 .l.tyuzn. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an at.y 1u1vzfl n.ngle 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 6.d4du)u,m*i4 kvx u7 pt0 $^{\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 steep a cpwqd;d w 3 )i)3- tmgzqx,yrb)p6)hl4ois)m hill can it climb at a constant speed of 75km/h if the frictional iy;c)bgptxw) i ),zwl -mh )qr3dm63pqs4od)forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box ap0 y6):ujjwxpffl+v8ix. 6g slong a level floor at a speed of 1.2m/s if the:8s6xpp).gf u0wly +i j6x fvj coefficient of friction is 0.45?    hp

  A bicyclist coasts downip.)sviat s;k+kl /ib(:e w, 5ttl o(y 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 buio wx6g vvlj.0um r29i,lt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but rem9i0 o6rxg,.jlv2vm u wains 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 (x / 0xn),au5q ot anm(gwao7qground, and the remaining four shelv5 o wa(matxug/nq(a, 0 7q)xones 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 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 famousjx62jhkd+ d 6a long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the62j adx+k6 hjd top 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 sliding6 aktc 1tp--si3ha6 wg(fap *d without friction along the looped track shown in Fig. 6–39 is to remain on the track at s a3*htdf1aga6(p-k6tci p -w 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 without his parachr (zvm2wb6sm 698 h 6tlujgd+qute opening. He landed in a snowbank, creating a crater 1.1 m deep, bu jhs r9g66d( mzbl62v tw+8muqt 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 torunw8dq */6m0b aj.yo a horizontal cord of length L whose other end is fixed (Fig*wr6. y8n0 /mqadujob . 6–43).
(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 climbsd:86.tw(jx owg dvo to69-z1xv7aj xm to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an e agx 67 wwvvj8(.x1mooj-9 d6 tdoxtz:levation 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 67 lg2dgrb-hh)-pfui 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 can move 47,000 pee musre88,y+ uople per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neede e,+eusum8 y8rd.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before s*0xd cyim mxkv-wc5)p8t ls/4triking the turbine blx8/ct)5xy vs-mipcd* mkw4 0lades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), the difqek094pm yb*l ference 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 dk q*e0 l9by4mpepend on the size of the loop or how fast you go through it.    mg

  (a) If the human body -p uilc 0/ cg0msfzwf06jp*a 8could convert a candy bar directly into work, how high could an 82-kg man c-jg w8 *0plfczsiu06 ap cm/f0limb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward an2 jxotc5xpsr8y:p8 u .gle 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 bay:7b ly pd e(j)ga1/ sto3krh)throom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read akb):dhyg )1/lpo ts(yejr73 at its peak?    N

  A 65-kg student runs jw3t+xjtx6:glw ehz,q xq 132 at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his veloci x3qg,wjzwxhj62 q1e tlxt:3+ ty 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 veri b 20s5s osa,ht99 p*y*u qnoa6in-xdtical distance of 5.0 m in 9.0 s. What mini*-9i,ssdahsp baxino*uy 9q25o6 0tn mum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pubipo5dz rv+99 v4oxjr+c 4a) gmped by reversible turbine pumps from a low to a high reservoir. To stoobzrxj4++p vo vc4a9 i)gr59d re 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 is the spr6 k /dvwx;b,uxing stiffness constawx/ u6;x,vdkb nt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up ye)s 0e-4qs x6j vg)hxa 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 accele7g7mio o: 9; 2ar puzyrvxa*2erate 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 neglxvg: oa*u2 2 o9;rz7iearym7pect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient wal9qonxy-(( v7j+ +jzu r,1cexaacx jl7ks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an anglecax77(z,j1v no (ry9jax e+ux+ -ljc q 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-knw hv,o/qn ;t g..aaw4g rock vertically upward a distance of 500 m, what was its velocity when it left the volcano? gawvo/wh ,4qa; .ntn. $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a r+;h qd*ucod yhn) m8/uate of 95kg/s (a) If this waterh/c*do yn8 hud+q;)mu wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s