In what ways is the word “work” as used in everyday language the same as tei +1l5kyjbp+hat defin e5y+bki+pl 1jed in physics? In what ways is it different? Give examples of both.

Can a centripetal force ev) 95g:h x; sfq5vj; t0han;ognfqtm r+er do work on an object? Explain.

Can the normal force o e cdl -.0.sb9jhkxg(fn an object ever do work? Explain.

A woman swimming upstream is not moving with respect tg4z4j *dg)ctcnvgh 7 +o the shore. Is she doing any work? If she stops swimmig4c4) *c v7dn z+hgjgtng and merely floats, is work done on her?

Is the work done by kinetic friction forces al(++whsi7y guaways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out frsg7u+ i( hywa+om under them.]

Why is it tiring to push hard against a solid wall even jx2 qz:sa 1f+z n2rfa(though you are doing no wor22jrsq1:(xzff zaa+ n k?

You have two springs that are identical except that sprisf q23mhu) f nr)g16lyng l is stiffer than spr nq) 1r2y)ml6uhfsg3f ing 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 is free 36-lh , o.6czrabaa hmto slide on a frictionlesz 6.alo-3h m ,hbrca6as surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential ene00j)syl. -gs1 uyus2bc yy yb)rgy change when you jump as high as you can?g ).by-lsyyyubsuy) j s020c1

In Fig. 6–31, water balloons are tossedyf8 v63lr mqa) from the roof of a building, all with the same speed but with different launch angles. Which one has the highesav)lmf 3q6 8yrt speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heh4/fiw*5c idx p. uk(qight 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 downw/dc u iq*f5i. 4phxk(ward 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 uprightf j- o0ma i(b1wtw-uj2 on a table. If you compress the spring by pressing down with y 2ouw-fj tba0jw(i -1mour hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a s 4zy)xbqmu)l9 teel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury th)y)l49bmuz qx e instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wate : or.c p0md/ n,twlqj4x+5hnyr at the top of a waterfall falls to the poo,+n nt5.o ldhcp:4 y mrj0x/wql below?

Describe the energy transformations when a chil+1-54zddpvy 8gka8whdulc pr+e v0 7ad hops around on a pogo stick.

Describe the energy transformations that takekf5p4.9 pi xdxrtn;6p place when a skier starts skiing down a hill, but after a time is brought to rest by 9kd4;x.xr tfip6p5p nstriking a snowdrift.

A child on a sled (total mass m) starts from rest at t3s )(vmg+mjqwhe top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, avm 3+qsgjw()mnd (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pa,hv- h5ps5 ntgth rather than stepping on top and jumping down on the other side. Ex5hptv,s -hn g5plain.

Two identical arrows, one with twicea3n c.tyx0sb0 the speed of the other, are fired into a 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? Explain3tsbcxya0 .n 0.

Analyze the motion of a simple swinging peno-gw3 s1bie2rwj2 pkm 1z; kn1dulum in terms of energy, (a) ignoring friction, a 12imr1w2oe;g1n kszk3 -wbjpnd (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height1* ywt21huxin greater than its origina wnu1x2ih1*y tl height? Explain.

Suppose you lift a suk,1s l0fxzs*//u3jsbupx4n uitcase from the 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 more complicated path, (b) the tim* n/flsu4,s1bxsx3 u0kp uj/ze it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed raj15vz u soyh4y(j: cq)ther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb smx)v5rp ,whvu0 0ndq4traight uvpdumwqx) 50 4hvr,0n p?

Recall from Chapter 4, Example 4–14, that you can 1)adojd+ kn.or:eny fw1/ t+ruse a pulley and ropes to decrease the fo)dt o1 .da k+ n+ry:e1fj/wrnorce needed to raise a heavy load (see 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 gravitational force when a 26rg(zztatuv hcarycv 7120 4)2 5-kg pile driver falls 2.8c 20t r)r 7u(gv1a4azh cv2tzy0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is :a(adaqn39 / ugsg n4hrequi4a9g:aqh 3(gdu/n ns ared?    J

  A 1300-N crate rests on the floor. How much8a:zc1 ss(d2 x 2wlswo work is required to move it at constant speed (a) 4.0 m along the fldzo1s c(las8w2 wsx:2oor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moq,r815subx j vv7a.znvers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficientvqzj,x8 rv 1 5sua.7nb of friction was 0.50?    J

  A box of mass 5.0 kg is accelerateg/oc/ o;n4dhf d by a force across a floor at a rate of for 7.0 s. Find thh4fo ;cg/d/n oe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mud9+c4/6gc6 9 bpcp(bv wx4x uba3stxr5 kjq,gch work is required to stack them one on tpt,c6r q gax p g3vskb+d/6bwc(u49xxb c49j5op of another?    J

A lever such as that shown in Fig. 6-a4hx7 r :4pvs9h2 urlp35 can be used to liff objects we might not otherwise be able to liff. pp4 2 4hrlu:hasvr9x 7Show 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 f ,t(zdhqh37 rnx4mft99m,sx and is kept from accelerating by a man who is pushing back ox9 t(3 9hnx7t4mh,fzf s,dr qmn it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter ofy9xhi)r fxm +++m (f 1gsdpei+ mass M an acceleration of 0.10 g u ixp f+mx+d)9shr gef++1(miypward.    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 that ncj3 wn8qb, 9h$d_{\mathrm{A}}=10.0$ 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, v8vo ac,.3rl+6en/ xy*yy iyrg aries as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0xoneg+ .8ilv3y,/6a*r c yyry 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 ;hfpv+;gbm/j particle 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 oxyvtrmg5hvk;s +a +*,gs8i wc0og p m8)cgen molecule, 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 what factor has its speed in) gyp o0 bht074bsola9creased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is reqvrqq 5z,k zc-x4 m: x/vamag*/f*nki ,uired 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 t+ dod,,yms kv,o 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 exerts an j* eu5k72 d2c;w abmja lu:rihs) (nrm,( uxj;average force of 110 N on the arrow over a distance of 78 cm. What 2u5bwia ,j; d)(l2jech asu n;mur*k7(:rxm jis the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glovee6zz19 ohol pb1 um/x; backward 25 cm when the ball is caught. What was the average forceu6h1x zz moe1pob9; l/ exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what8e st:g3 tso-d factor will its minimum braking distance be increased, assuming all else is the sa o :te3gt8-sdsme? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measns0mh/ d2-zg*su ak-rure a car’s skid mark to be 88 m long. The accident occurred on a r *-ha2-0m/g ukdrsz snainy 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 brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass .j j78:o6bqlb ue0jrsof 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. e:8jbq6 bj.j s0lu7orNeglecting 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 doeszvo+.lxh rx8k *wq:k7 80.0 J of work on it? Neglect air resistak l.7k+: hxvq8w*orzx nce.    m

  A 285-kg load is lifted 22.0 m verticallyr9 *gh nsry. lko47oe* with an acceleration by a single cab9gonrlsy* ke7*orh4 .le. 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 stif+bb.rmf pzsc0k9(3 eofness constant, k, of 440N/m How much must this spring be stretched to.0fbzo r9b +e3ckm(p s store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.27 ;-loz2tg8oxo 9gvxu m higher. What is the change t7ovux;o-zg8x29 log in potential energy?    J

  By how much does the gravitational potential yy5(e,pwmxv:,of:z k energy of a 64-kg pole vaulter change if his center oyemwf yxk( : o5,p,:zvf mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontalk6u3jwv8g1d u surface 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 spring stiffness 61u3kvwu 8djg constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.1.)l5+ 7dyx gqfilszz, 0-kg book from the ground so it is 2.20 m above the groul lsd5y)g7z .qx, z+find. What is the potential energy 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 elevatiu 8 ft*42pyilhehg/* g)7gjz1-kzh ijon of 1600 m and climbs to the top of a 3300-m 72 yi 8pj/jeghilzu)th4k1 f-* *zhggpeak.
(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 hang4mo2l)dp),ya f)jm ius vertically next to a ruler. The end of the spring is next to the 15-cm markmj)o)uy, m2dilp4f )a 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 Tarzan, is running at top speed (5.3m/s) and5s8xf0. qfz iq khubj/ z*hw1/ grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward?5w. hzs8f 1xij/ z/*qhbquf0k    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35.54cij5s9 m56au exnxp0$^{\circ}$ 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 up9e(c 65 wg/pdve al-ox 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 oe)k jh h87-/mbzpj 61uny5mi energy is transformed into gravitational potenti17 o-z)mipkn b6 hme jujh/y58al energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform w1tuw97ucix;la zd9so de0+g7 ith 9a zwxisd7tul07;eg+91co dua 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 sprin- vlm1 ld9)vfjg stiffness constant is 950N/m is attached f 1j l-9vvd)lmto a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped tracks)b9jb h8yuv./) auvz shown in Fig. 6–39. If the block is to remain on the track, even at the topsv 9b))yub.j hav/8 uz of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness consb;rlc qk jiq)vzf+3)*1w u:vstant k), Fig. 6–40. The blockz ur*; 13lvws i)qqbcfj:v) +k 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;9 ush6kv4bk :j f(b4 ctx;jhe bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a fkt( 6eh9;j4:hs4bckb xjvu; 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–c/ k3dacya128:qo xq w41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculk yadxc21w:q aq/oc3 8ate 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 ;949 sa-a6 ld4gzv nu;qoqg vqat 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 placed at the bottom of an eleva(p29nv4w6opmrd1 y*3m pfp6 jb v1eujtor 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 cons4uvm2y pp6jb6vmjp1eond1 9 f*3r( w ptant 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 up a 7.8 d4 1h9zam(roeyz3;ju$^{\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 trab vo/ l1n.o1cg2ha:ql)gq yf 6veling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is prodql gv o qgybh.21a1of)c6:l/ nuced 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 wu.p 7* ttn,o7 qhwd0thith a speed of 2.2m/s How much thermal energy due to friction was generat ,qdw 0*thot7nhpt. u7ed in this process?    J

  A ski starts from rest and zd0zs9 sxbj+.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 fromzfso 7q)8w j3kf )j7ig 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 boub9pd9nlb/jy(c5 23v l kifv4 hnces back to a height of 1.5 m. ic(9/jk3byn dpb v29fl54l hv
(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,;)tw; knotei 7ypb4x n1fn;+k is pulled 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 frictioni;ntt pn ;+)y1 kekf7x4;nbwo is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poicz(tyi7z b*:nnt 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with nti*z7z:cy (bwhat 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 steanfla:3 1u )ihou7bnxa9s5;n jdy 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 lightb8; gke*lrhd ml(0r5r xiyu 4( horizontal 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 equilibk u (y;dl0r b85xm i*r(gl4erhrium 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 horizont7onavh-k;m9q vj ; ox/al 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 /x;o79 q;j hv ok-vmanis released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space m il b-eoucw-g 5dhaf2-2f-*cshuttle 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 be2m--d 5b2 cc-uwe*l f-gfhioaen 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 aikflr4:l6vx* 1750-W motor to lift a 315-kg piano to a sixth-story wind*6:4rv kl flxiow 16.0 m above?    s

  If a car generates 18 hp when t2-px2ytzdv / /t7thdf y,+xcgraveling at a steady 88km/h what must be the average force exerted on the cav 2y,htxt-z/c2 +dx/ 7tydpfg r due to friction and air resistance?    N

  A 1400-kg sports car accelerateszm;z7t9) f v5pz vgt+qma3q9u from rest to 95km/h in 7.4 s. What is the average pow)f q+;zqgmvuttp93 79zaz5m v er delivered by the engine?$\approx$    hp

  (a) Show that one Britishq; xc;va)j2lh 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 iup -pdv7ko :ih,9af8 are often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down fro rxcnb6; s 7jxyef y2+kb58j:gm to 65km/h in about 6.0 s on the level w5cfkx 2ngjrs x7+ey :6;bbj8y hen it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do injykz.*+j /jp.hl., ipx .mut v 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceleratafl wf,k 9e -1lb lx0hdw9jo+4es a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what1o+04l9 w, klhj9- xldfefwba average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of warhjgpqq6(e0u3 wsd * 0ter per minute through a height of 3.60 m. What output rating (watts) should the pum peg 6(h0sr*wqdu30j qp motor have?    W

  During a workout, the football players at State U. ran up the stad7vba zj- tgp0c+9/w iiium stairs in 66 s. The stairs are 140 m long and i+/ 7pcw9-j z tbvigai0nclined 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 clim4iv d,v .tq6xf uq(5iqb 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 1p 1/upuy *s vav-- jhq7ejn2x/20 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to / nju 1uvy7e2*ph-xpa /jsvq- 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box ap/y- x edztn*4long a level floor at a speed of 1.2m/s if the coefficient of fricti y*zxdnpt-4e/on is 0.45?    hp

  A bicyclist coasts down,10 p51i zksenrn sky0 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) iwft53-md7 m+ okt tj+bumpers” that are designed to compress and rebound elastically without any physical damage at speedsdi+ -7t3wm +jtm5fokt 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 firs 1ri-cbxie1p 2t shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf rxp1e- 2c1b iiholds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Ojflb vdj58 jhe )wf .zp95p/k9lympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at.jfl9 vehwp85z kj/j9d )f5pb 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding wit 1i7 dgwvz.8pyhout friction along the looped track shown in Fig. 6–39 is p7w 8v1yigdz. to remain on the track at 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 aizu:s.x1afi tsb hy0laaaw :.03w6ad1rcraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assumla:. 0sh3s a1fa1:6uwiz0.txaydawb ing the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose++7 zr hvqw/lf other end is fixed (Fig. 6–43).w+ r /hl+qzfv7
(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.zv6 i..jdl c,j The climb is made in 5.0 h startij. cjidlv 6,.zng 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 920-kg elevator is 28 m above a huge spring bpl 3 jujkzov 50+:mw4($k=2.2\times10^{5} \mathrm{N/m}$) 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 inl8*u k) cdix5u California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (verticalx5)ul *du ick8ly) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fallr5wp w1po9 p4e:du a.ms vertically 81 m before striking the turbine bladramp wd.w5o4:1p upe 9es. 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 (Figzy.wztfle8mi )ha . *2)2zcha. 6–44), the difference in your apparent weight at2 iml).8h* z zf)hc.w z2aatye 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 loop or how fast you go through it.    mg

  (a) If the human body could convert a ca-sj+gf p 2 x.cyyis+f/ndy bar directly into work, how high could an 82is/ygp.f++f jsx-cy2 -kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an xxja+c 6jgf 9(upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale yz y/ju ;;rr:lcompresses 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 try;y/ruzl: j; he scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out ohx)2 int/df7 qiut1,aver a lake (Fig. 6–45). He releases the rope when his vet ua ,itix7/12dq)hnflocity 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 verti28ksalf b.q* v4f 8elx3g-vtgcal distance of 5.0 m in 9.0 s. What minimum power output was used to accompl .2k ql-ffv*eb4t8gxlgsva 3 8ish this feat?    W

  Some electric-power companies use water to store mzvq )dj;26d(pq 3o c *l-n8hldtz8qpenergy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.qz-8cq* 3ztj(onm) p6v8;pdd2qhll d 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 spring0p (x,wlv;+, (djpe x-me zsua stiffness constant for each of v0 lejwpae;-d,m (p+usx,zx(the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough: j-ca o)v)qjaigky ,/ 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 s, how long will i.wm4-vx rem7yt take to accelerate from 55km/h to 75km/h Assume the power staymw-rx7 m yve4.s the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)iu9-4c lev8 (asw xa lx((hrqnxy2 6b(, the patient walks on an inclined treadmillu((exabvax lwiq 2l46h8 ncx-s((ry9 (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 50t: p:o5 vyzu1a0-kg rock vertically upward a distance of 500 m, what was its velocity wu :5t1y: azopvhen it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95stz,2:wt+)b5mg aa zcno ;7n xkg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power output? zb +tcna5zn xs:,oga; w2t7 )m    W
(b) What is the speed of the water as it hits the wheel?    m/s