In what ways is the wod*..u-qril +bckii f/rd “work” as used in everyday language the same as that defined in phys fudl/b* ..i-kii+qrcics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an objic/ g))k5t7p3r wnga l mv2l*aect? Explain.

Can the normal force on an object ever do work? Explain.wa . (h7+elczz+ 5nwlh

A woman swimming upstream is7i0yhhd; j0 7rpr0 es01xryy l not moving with respect to the shore. Is she doing any work? If she stops swimming ar7e0 0x7;0s10pijhryl yhd y rnd merely floats, is work done on her?

Is the work done by kinetic friction forces alwa s-q) 7ipyffy,vb )4vzys negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out frov)bv)py4 y -,7 zqfsfim under them.]

Why is it tiring to push hard against a solid wall even though you are doiebfz )yaowu q36w0 984aw2ji dng no w d ioewu849 fj 0)aawyb2wzq63ork?

You have two springs that are identical except that spring l is sztgj :uht9f,uhgv2 :5 tiffer than spri,h: jz9vhuggt52:ftu ng 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 isv7;,c t8onb ks free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, an 7tbks8v; o,ncd 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 potv eb:ks0k15g bential energy change when you jump as high asb5v: es1bg k0k you can?

In Fig. 6–31, water balloons are tossed from t3w26hqt,w5y)nsx qnk he roof of a building, all with the same spewk,6 3hnn5tq2)wyqxsed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point 3qzw6d :o1g+ar3( ffm nit,fmthat 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/zq:( 6 f3wfr,dg31mft aoi+mn 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 uprigh0o-coitbp- 8kt on a table. If you compress the spring by pressing down witbck p -o-0oit8h your 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 ce;;ax esbr +w)zci+ o0tiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball ag)b+ eawco;zt+x;rs0 iainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water k)9mr v k oy(8bhwc/1efjk1q -at the top of a waterfall falls to the pool be hvckkm(e1)j-k /1qy b8w 9orflow?

Describe the energy transformn kjge +8qm36wations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starg:5 5apldvo3vxs(xtm- gu8 4qts skiing down a hill, but after a time is broug upl54g o8s3m:5 g- vqvtd(axxht to rest by striking a snowdrift.

A child on a sled (total mass m) starts from r/(9bubw*up3 d4 x gxicest at the 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 ubp34 bxu(gd w*i/9cx no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to s:.o m-h wsgc/step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explain.gmhsoc -s .:/w

Two identical arrows, one with twice the speed of the ot-,5mlggzs oh42ah p c9her, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows2msp,oc4g h l9 z-5ahg, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendi16pm z*zi-odulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock iio6z1- zdp *mhas to be wound up.

When a “superball” is dropped, can it rebound to a hha3q. f,z1tps eight greater than its original height? Explt. a,pqfz 3h1sain.

Suppose you lift a suit-wg h98hoa;xjv p au77case 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 ava8xj97h7u- w; ghpoa 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 neeribhfj2 l0/h d mg*z19ded rather than the work.

Why is it easier to climb a mountain )uis305 iuubybu0 /m (4oawebvia a zigzag trail than to climb straight upe0 yu bm(a u4)uuios5 w3b0/ib?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rok. yfko x-o5nx;khqei 3p,f.(pes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled upqk.yknx, . ; 3xkfio5ef-hp(o? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fall9rq066iv jxs as 2.80 m?9ja6i6sqx vr 0    J

  A 65.0-kg firefighter climbs a f+tf dbwvl, t8.tu.4j nlight of stairs 20.0 m high. How much work is required? t.8dtufw l, +j.t nbv4   J

  A 1300-N crate rests on the floor. How d662 4uryd+ ibhgtxp*much work is required to move it at constant speed (a) 4.0 m along the y g62ui*rt pbx4 d6dh+floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizoe7.qp;q ar6,2j k wbm;nv ta/sntally) pushing a 160-kg crate 10.3 m acro.q , vmeb7 skaprwaj;q t/n;26ss a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accele5,q vyk2 :i g.xpsivr-rated by a force across a floor at a rate of for 7.0 s. Find th:r5qi vp-xisv ,g.ky2 e net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table.f; r*pfwxn: xcq f(*2v How much work is required to stack them one on top of ano2 *nxwf cffrxp; vq:(*ther?    J

A lever such as that shown in Fig. 6-35 can be used to liff object 1wh,ahh38rans we might not31 ar,a whhh8n otherwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 2880x qt7om m8ka° incline and is kept from accelerating by a man who is pushing m 87xmatoq k80back on 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 jjj g: 3ze4x8s 0lc3pjto give a helicopter of mass M an acceleration of 0.10 g upwl403g es3xpc jjj:8j zard.    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 linearp6w 0 bxc0 m:dz/mogj35myzda jf y779 and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, var4 1rj c pbc5ti9o)vp2nies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) fro4cjn)cp9o21i tpv b5 rm 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 the0qqpxtgyo8 55 $+x$ 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 moleculesl fl5y l).1r44wqoll)vrhu+oja; ; s , 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 spel1of)y v(9ju led increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stodo9h etmh+:4z hwy d+8p an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgu yc0pmv2 ;r5ub,m9ohcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strinm6,pyj64vd dw+ a + ,e8wbo0kkynpv 5wg exerts an average force of 110 N on the arrow over a distance of 78 cm,k6pj+0aow v +ym45dv6,8pkde nwybw. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backe-x. xe ob/z /ki*bvk2ward 25 cm when tx ozx 2i/b kk./e-vb*ehe ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by;a9h -obbxr:gs+ 5uq g what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the drivsb5a :q +-u;gro bx9gher’s reaction time.

  At an accident scene on a level road, investigators measure a car’s so .uuwoank5 :9el4ik 8kid 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) thea:9eo. u li5kkw84uon brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mask yht5,1oryqhl3-vh7j fdm4,s of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the3 jq1lfmh54ydovh ,rhy ,-kt7 distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown sfnj-ys) e;qiues o -kuhrp)*h*xlg 802 wd: k+traight up by someone who does 80.0 J of work on it? Neglect air reln eu*o20k wuk*e -i sjxdh :qrhyp s8fg-+;))sistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a si7fiu- oh/c (b -zvu:xgngle cable.i-z7 g/hb-ou c: xuv(f Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must thbi;lp1w 4s gd1d g3ri -f6ei(ois spring be stretchf4r wo -s; dbi1glpe1i36gd (ied to store 25 J of potential energy?    m

  A 7.0-kg monkey swings frek5 8w2 rzdn*yom one branch to another 1.2 m higher. What is the change in potential eneryn e z28krw*5dgy?    J

  By how much does the gravitational potential energwi42jrfgc9:t,n+ k;b ,l9vo cltd kv0 y of a 64-kg pole vaulter change if his center of mass rises about 4.ol li t n fd90tg,vvwb,kc;+cr9k4:2j0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sehb8(r tbiulsb8l:65urface 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 constant of 6u:hl 8tis 5er8bb l(bthe spring?    N/m

  A 1.60-m tall person liv. dfov74n qd4fts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potentd4fodq v vn47.ial 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 elevation of 1600 m and climbs to tif 0;zfi,qq/w he top of a 3300-m peakf;,w/ fq0 iziq.
(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 vertically next to a rulez-g-r ch42 rwygffz os;:*0vs r. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now :fvr gwsof0;cz-y z-2gshr 4*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 s1e:dp gas9j l,5ow7np2 3nrhjpeed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. Howh9ldwp:1, nej7 s32p o5nag rj 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 frictionless 35,bsnl cf c wq,*dh h)0la1e0)c.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 frictionless 2:svb o xc6)qq;8.0$^{\circ}$ 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 kineeqdl+7d 9qg j/tic energy is transformed into gravitational potential energy without the aid of a p+qjd97de gq /lole. 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 platfnppx6x l+,a fzjzbb8*f4 u-z 1orm wit f1pun+f,jz8z x-bb4x6 zp*a lh a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignorec.9bsc. / zz 31vckt gypv31rkf8n -ht its mass), whose spring stiffness constant is 950N/m is attached to 3pf 8kt1 srzhgbycc.3 zvtk/n.- 19cva 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 loopedrtag pl6r6ki 2s;,-zr track shown in Fig. 6–39. If the block is to remain on the track, even at the top -6p;,rslit g6 2azkr rof 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 of6z,; em rw(fyv w;p as-;posm-s c o1f3k1ew4x a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaxy; pco 46zpe,(ome311-sswksv awwr- f;;fmcement $x_0$ 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 bt (3dm 4m t1zkqh .b2/pvmg2cvungee cord whose unstretched length is 12 m, and falls a tcg3k4p(/2.2ztv b1mh tdmvmq otal 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. 6–4bm 8 +iua 1dp6m:)f tg4ttnyo81 is dragged up to point 1 where it is released from rest. Assuming no friction, calcula: omm)pfg8t+bu4dt8nt 6iy a1te 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 an angle mx 0hwdr( qlwsxam9 b2u g6 tkq8s68*.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 eleve*j(2klyu 9baator shaft. If the elevator cable should break when the elevatoba k*29je(uyl r is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle-yx;,6f m hlqc 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, eaja6b8m2ghd)l+at y2mch of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this colltm26 j) 2adbgl+ ymh8aision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom witihy ;/u(g bdaqa(y j4m,-.d vvh a speed of 2.2m/s How much thermal energy due to friction was generated in this process?i;jdvdq-a b (yg(m,vuy4/h. a    J

  A ski starts from rest and s5nb: hpat(c4 * uc)bv+ 3tnvralides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the ground.xrk :( :cqfup13d+r 671ku q3or guiww
(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 m9i (i/kn6ov h 6dsum2back to a height of 1.5 m.oski/v6d(nm6h9 umi2
(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 frz.u g.yi y)an 2y-u6ukom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for th6 uk2..i )gayz-un yuye next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed oqybl: y6n- zg,f If the average force of friction is eqz bq-n 6,ygy:lual 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 fo4/ jikdn.ee8 5w7sc x5dwl oq9r(gn+ rot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firml 1a97jv58xuf)( jbr,xbv igy oy attached to a very light 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 tx u)y jgab1v i,(r78b f5vxo9jhe equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attachedxf iy 57ul3kl v+m,4d;fnekm 8 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 compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stl + ,ymf;ki7l8x3kmfn duev5 4retch on its first swing?    m

  Early test flights for the space shu ihsq89 c va54/j6qbmll l,sch e4qur-fz,)y+ttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500kz/ rquai,q cs+6ql 4e4-jf9hc, 8 bv syl5)lmhm/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 6lst mk8dt l(m:xm jl(:gl;( tlift a 315-kg piano to a sixth-story window 16.0 m al(l;d(t8km (m lgxlt:m 6ts :jbove?    s

  If a car generates 18 hp when traveling at a steai7f kq.s(v gr;4zs /lzdy 88km/h what must be the average force exerted on the car due to friction and air re .s ki/zlzqrg ;f4(s7vsistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h:/7b-zq v(zn2xh9sjv n )ls(kmy+b sb in 7.4 s. What is the average power delivered by the enznn-s vbzx2hbl)m+9 7ss:kb jy q((v/gine?$\approx$    hp

  (a) Show that one British horsa* (6pw)tnrg)hx(mivepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hours 8rg kk6-+qh rq2h(pl 8vg(kes.”
(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 1150e 8ls eu06n;bgzszq/* -kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hpnesl 8qez uz/0gsb*;6) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mot6ley bl f *2.p/u:nxudor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s kei/tb+d5-q l 1be gp5If this motion takes 1.5 s, what av e5/ +dg-belt1kpqb5i erage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water poda wqn*-d* r4u-o/bcer minute through a height of 3.60 m. What output*o -*udb4 dwaqonrc -/ rating (watts) should the pump motor have?    W

  During a workout, the foj l ;18jcav6mk8fv pf,otball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclinv8jc68k afj vl ,f;m1ped 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 3,;pidyqcx u( climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can iposst4oa j1 ;y0ct w)q7e*;m ht climb at a constant speed of 75km/h if the;0w;o yjh71ose*m tqca4) pst frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag ai*m(0wxdvf96bls 4 u f 310-kg box along a level floor at a speed of 1.2m/sdlb wf9 xms4u(*0f6vi if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a x5k)kyn 2b qr,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) bumisy6 3mpmw p68pers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumppmp 36 68myiwsers 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 10.0at.( z0dcok:l cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average bltd0z :.oa (ckook 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 famous long jump (Fig. 6–42) in the 10;7moc6pngq c o zzsll i2k6m76uui),936 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 nee,zo)6m6sk iq0c7 l7; ip nl6g2uzu ocmd at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding witqc(quj30tw efe 7eg/r3 +tm y9hout friction along the looped track shown in Fig. 6–39 is to remain on the track qe/wj37(t fe qmy309tegu +rcat 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 pa* q7 jv z1t/ 1e:r1gytxmg5qahrachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assmeaj1yt* /7q hq 5gg:rv 1x1ztuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed (o k(9u h8ig50mhae6 fzFig. 6–43) 0e au89(5hz6fhmio kg.
(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- bmd d8go))yp *o/h7ugm-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculat du)8g/m*yoo7b)gp h de
(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 8l- jnwy2;:gpb8 zxkjyg 5y(j 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 +z00 lc .3sz d7oiee d(l;swy3tpu ga847,000 people per hour. If the average lift carries people about 200 m (vertically) hi 0szecszulpg0ty+ei.( wa dd3l;o 738gher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 65k: 161l /aj5aremcqf*uu yb 8n0kg/s and falls vertically 81 m before striking the turbine blades. Cbaj56yak l*e cr1m:qu 8/nf1 ualculate
(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-omi tx.01 lvjq7kfupgzu1 + 9–44), the difference in your apparent weight z7q.l u vtxmugi +11jp90 -kfoat 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 candy bar dir;9,r,jhs(, hdgoojpd(8ogjgkp 8;uoectly into work, how high could an 82-kg man climb a ladder if he were f,ggu;p(g hjo,d,odks j (oh88o;9 j prueled 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. q1a*/mokhp hneac 4230$^{\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 scalesved.6 9fded .qky7.xvniu cg880p, l compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on txyd9l d8vcupkd.6ie 0f ,.. 7gn sq8vehe 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 (is )43at j2p7r t-:hmof+a kgpFig. 6–45). He relso)pt42hmg 3-j:a7atrk+pi feases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete kr;*mz0*c -zhtkqd1 yq cd/;iclimbs a vertical distance of 5.0 m in 9.0 s. What minimum power output rdm ;kkcqyz*i/hc; *z 0tq-d1was used to accomplish this feat?    W

  Some electric-power companiesz v6rj2kn zo6h7si *c3+ue33 wkx mmp, use water to store energy. Water is pumped by reversible turbine pumpswkm6pch6m niz7,x23re+ 3j3u k* vozs from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half.erovma a28cl4;oqu 5 l*7utq: What is the spring stiffnesc r5ovau7q :;u4*2eqll8atmos constant for each of the two resulting springs?   k

  A 6.0-kg block is pu chwxfa+ rvrd+mf,mz0r (r7 +:shed 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate c0n(g. /8hust5vzwa u from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate( 5hnus0 awz8./tgu cv from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “strdxo) 2 tsh-hkyhh 108 3peejd*ess test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angj he-ophx2)e3hky8 dh s d*10tle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a df8xgpu z4g08yt;kq** l i9uvmistance of 500 m, what was its velocity when it left the vou;iyv t*p0q*g48zkx8m9ulg f lcano? $\approx$    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 ,6fa hnar1 6+dj fnn*wkbko;d1 pwy8, of 95kg/s (a) If this water*a,1ywdfjd arnb 6;pk,8 1fnn6k+how 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