In what ways is the word “work” as used in everyday language zea qr c1fms9u nez-,(ouby88ee4 ( o4the same as that defizu oo -8qbzs aee144u n(89eeryc(,mfned in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work onixa sx4j ovl1xy917+p4 ycws2 an object? Explain.

Can the normal force on an object ever do work?c dwyi7(nu-t l3j(k 0m Explain.

A woman swimming upstream w-e urv l,6ww)t p6+dzbed,j13bv1c mis not moving with respect to the shore. Is she doing any work? If she stopv6tjdrew3)6+w ue z 1m-dc,p vblw 1b,s swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwa 3 l6 pqng5sz 5:0xd89uzkroqzys negative? [Hint: Consider what hx5 d39zznqogs5puzq 68 klr:0 appens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wallzg15a a4c3 nqo even though you are doing no work5 aq1onagc34z?

You have two springs that are identt02prn02c nbmp7dz bd .ps-p5ical except that spring l is stiffer than spring 2 rpncp20b5.7p20t dmsn-dpbz $(k_1>k_2).$ 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 constahhc2 s3p;wa18r zoq,unt horizontal force on a block that is free to slide on a frictionless sw;1 au8z2q,r hoc3hp 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 gravit;8 yuy /2yjpicational potential energy change when you jump as high as you cc8yy; y/2jpuian?

In Fig. 6–31, water balloorfm 012kl slaf;q:(a +l.vemnns are tossed from the roof of a building, all with the same speed but with different launch angl+k:lvfl1nl2ema .s q;f0m(raes. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its loe /dwqqtrxu2)a1x/ n rjws::8west point in r2:uda8q)xwtn 1q/w:xr sj/e two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tableb8uvhy2xkv 1; . If you compress the spring by pressing down with your hand and then release it, can the spring leave the tax y28v1kubvh;ble? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The in0hhtv2 ap- svxu3uz,,structor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release v,xupz2 h0,sa-vuth3 the ball without pushing it. Why?

What happens to the gravis.rh11 ulyez (z+v:le tational potential energy when water at the top of a wateryz1 l .es(ruvz1+le:hfall falls to the pool below?

Describe the energy transformations when a child hops around on 2cf rww,4*bve a pogo stick.

Describe the energy trafsmj; 3ig2kl5;mi lfc( /tqvb;ipxijd 2a839nsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrift.(vmfk;mt; j22j3bqi39xfsll8i/d pcia gi; 5

A child on a sled (total mass m) s56vb8rir ,q dstarts from rest at the top of a hill of height h and slides down. Does the velocity at the bottomd rq6v,i 5srb8 depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pakxgew-. g moi7qju),x:y l21rth rather than stepping on top and jumping d:jli ) mex7y2x1u rk,-qggo. wown on the other side. Explain.

Two identical arrows, one with twice the speed of s5pfjrl )3t3gce,fz)the other, are fired into a bale of hay. At 353r,jcfe p)fs gzl)ssuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) ignorducvb;e4qossini)a : ,-w e:1ing friction, and (b) tae;:s4 iaq)u v iw-sd1e ,ncob:king friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater st9kfy- lr -bej ,sx6(xbuz4 2than its original ht6e(xljry- 2bs-zu4fb, s9 k xeight? Explain.

Suppose you lift a suitcase from the floor to a table. The workaz xidu 66)sy; you do on the suitcase depends on which of the followingaxs;u6d) zy 6i: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than s; hlu3 w/yjq3the work.

Why is it easier to climb a mountain abixq +*iw)(svia a zigzag trail than to climb straight u)aiqs+(i wb* xp?

Recall from Chapter 4, Example 4–14, that you can use a pulley an;jw69 bipg 8sbd ropes to decrease the force needed to raise a heavy load ibj 8;wspb9 g6(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 kwmvry1--g 0twhen a 265-kg pile driver falls 2.g y1twrm vk-0-80 m?    J

  A 65.0-kg firefighter climbs a flight of84n,5yukq h5lfgl 3cn stairs 20.0 m high. How much work is required?q8cg,lnnyh4l3k55 uf    J

  A 1300-N crate rests on the p s bnt2h+ gne(ya,4g-oo.bkl7)me5 sfloor. How much work is required to move it at constant speed (a) 4.0 m along )b7kyn ao45 sem.g+ bo,2tgpsnl-h(e the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontallynzol8b8vqey.;nx.y sl qt m :.eiz8 1s83tt y*) pushing a 160-kg crate 10.3 m acrosnsbttmly.1*n8zz.v83 eilqoqs8t ey.;y: x8 s a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is ac- bbxi0lqf-m 1px;s)ccelerated by a force across a floor at a rate of for 7.0 s. Find the net work do bxf0m;piq s-)xc -1blne on the box.   J

  Eight books, each 4.3 cm thi04gs8 b0 axezpi4a-cyck with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top oi48b x4a pcs0agey-z0 f another?    J

A lever such as that shown in Fig. s6mw m27susat9 s/9cu 70dxqis s f,3c6-35 can be used to liff objects we might not otherwise be able to c9c sds w ms/ms7,a7ut3s6qxsf0 i2 u9liff. 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 nof)t .-yhi 7nup7g8pm down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of k fpgp8n utiyo7.)7n-hinetic 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 helicopterc t3xmvjzq9,0 of mass M an acceleration of 0.10 g upwarm,0zqcx vtj39d.    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 axt b x2(t-a7lhpis 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, acting along the x axis, var aw87(ccvze2/ag r3i ckbnv3-ies as shown in Fig. 6–37. Determine the work do7av 2a8 ze-i(3rcnccgw v3b/ kne 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 partic*q +8crqxzcc( le 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 oxygenx10ajym*ql+pxu fe * ) 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 dou3 t.kgls2)s5;yy hv pawo8bw9 fjq86tbled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elect .a43ecvl 5l* ypb0cqbv4r7ngron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105k( zx-7rn3e ftom/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average fo/m f*;yr-54sle wikzprce of 110 N on the arrow over a distance of 78 cm. Wha p4*mekl ;r-if/s wz5yt is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s gl+0 /lrxlecml4 ove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glo l+4lm0 /clerxve?    N

If the speed of a car is increased by 50%, by what factor will it)-s0jtpssb0q s minimum braking distance be increased, assuming al)qts0bs0 jp- sl else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators mq),- .v4sqdjo5z wzweeasure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the w4.ejvwq zsdzq- )5,ocoefficient 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 of 0.25 kg is pitched at By the time it reachwc0ddlm kr,0 sdc*g 3 pio:40ves the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betw:r00 03 ciowd cgmp,v ld*k4dseen the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown s7w3)jnb/ b +bbb oof7k);z q4wp (mmvqtraight up by someone who does 80.0 J of work onq/joq7w+vm4pm)fk )w 3( bb nbbz;b7o it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vert22bakvjidk0 :ically with an acceleration by a single cable. Determine jv2k da :2bik0
(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 4jxapf4c;. sl + krl9ahw9;uy yi4o2/s40N/m How much must this spring be stretched to store 25 J of potential energy?y f s9u4 .9;ls+r/xckoapj4hiwa ;y2l    m

  A 7.0-kg monkey swings from one branch to another 1.5z a6-qz5 y+wjivf5 .ids1l73 xsy iat2 m higher. What is the change in potential energ iq575+ s3.vy1li zxzfwsi-yta5aj 6 dy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulteqb naa9 6p t9.gyt35msr change if hisbtq9p5s.na6ayg m93t center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on jrp xp4uw7ukdop( s43,j97hd t; ej(ta horizontal surface has speed v = 65 km/h when it strikes a horizontal coiledrwd4;u9 ,p3ps7p7 kthjjt oexuj(d 4( spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book f)b9h0bj 8 embg/ hn)thrj*p w6rom the ground so it is 2.20 m above the ground. What is the potential energy of h8nr )twgeh pb6mb0j */b9hj )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 td-kf s fceq5787qe; bgo the top of a 3300-m peaks-5c8kq fd ;bfeq e7g7.
(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 vertr ;ucehpf 6t+db;u.vgog /+.sically 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, wh p/bt.f+;ve;us+6ourg h d .gcere will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, i,vnnj3cmut ;0 8+qe8:tc xtaas running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree x8n ujtae3nc ;+m8v qa0c,t:tin 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 t gk23x csjvoj;)8 cd0from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a m9.o: uluuj/oshove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kz6msxq/ xwmt.. ye 7m- znu/f-inetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed mustt6//zqyeu.mfnz-x -.7m m swx 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 jn4 rjfp4ek6/ vertically upward from the top of a platform with a speed of 5.0 m/sj46/nep 4frj k. ($\alpha)$ 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 su-h2fqd0(p2l (m t.jf qbnt)av .r (fypring stiffness constant is 950N/m is attf0a( hd lfqtq)pv2j.nu yfbr (2 .(m-tached to 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 ipo7 h9p5-eus*4ckrcj1f 8u wlooped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose ra j4k7f 5is98pc1-ch o*e rpwuudius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring3c* zz rfa,k.u ;byt;;i kf-7ug0sv om (spring stiffness constant k), u;b;.k*a0kvr zy smg;ufoi,tc7 3-zfFig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumpesxa,1/ 7 3 wvex9vcolxr jumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of l7 w1v9ec,xx3/ovx sa 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 eo3g nqwtm3l(zbx97mqx7(v .where it is relemn x7lgq3qtm(xb 73z9.(vwo eased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown 466r9ehe lj yswith a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed)tzbk nqd*kk6 ;dh-0 a at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above t dq6k;0 )adzhbt- *knkhe 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 up a 7.8u bv yaf9jq(w4(h 4k4cej21 bq $^{\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 wngu :r, 8r gg/ezh/:sof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and chg,r n/wr eg:gszu:8 /ome to 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.:sq3 f9) l2z alzf;gzp5 m high and reaches the bottom with a speed of 2.2m zqa39z f:f)pgzsl l;2/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from restv 68a. jwivln9ea42 wz and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m9i s p* )t.btrl8-utem 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, a.y8 tm v2pnnt6nd it bounces back to a height of 1.5 m.vn tp2mn .8yt6
(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, starszracr g(/sr keg14xj*:n4x la(12/ gwzv.w rting from rest, is pulled across a floor with a constant horizontal force of 350 N. j1gr4wca2z:ksw*v1 (x z n./ex4r/ arr lg g(sFor the first 15 m the floor is frictionless, and for the 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 of If op . vod byb-u2d8*x0zthe average force of friction is voub.o y2d8 -b*xz0p dequal 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 ofp f 901eptgdd)n: lxk. a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attachecy*od7 1 2k:,g1uj qsqd n4ulud 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 the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between th 1u gjuunq, *c47ddl1koqs:y2e block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, /f9lhfc a:j ,6h/d3tt cgek,tFig. 6–40. The block can slajtkft3c 9c: ef/6 tg,d,h/hlide 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 stretch on its first swing?    m

  Early test flights for the space shuttle use- nwtnajkmr)cmnvd06b1-;02ah* it j d 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 (a6;*1j20-kcan-d wn b vtmj0 tminha)r) 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 t6w 6b6whajlt*o lift a 315-kg piano to a sixth-story window 16.0 6 bajt*6 lw6whm above?    s

  If a car generates 18 hp when traveling at a steady 8:-1sod1 wlu*0 yhkgctf )g xz0*qc1zv8km/h what must be the average force exerted on the car due t xvwo1qsfgz- yk) 1cct 100ld g*:hzu*o friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kmvtej c++jhm- stkug8d /.w s*9/h in 7.4 s. What is the average power dhcgesjk9 t* t8 m+/ju -vd.sw+elivered by the engine?$\approx$    hp

  (a) Show that one British uqa8.,ibwt iec 4i f+no7(t)khorsepower$ \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 n*/p-fjiamrucq 7re6:ku0y* 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 from n(sd o-p zp.k)p1 qy1e to 65km/h in about 6.0 s on the lpndy-o 1 p.(kz1s e)qpevel when 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 in 1.pgc)3t3r lzs80 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.p;lj0egtj w;sr.-4 dc 3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average poerj4ds;;j -wgltp 0 c.wer was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throuad8w3jwr 4 bz).oe:cxl iv6k5gh a height of 3.60 m. What output rating (watts) should the pump motor have?3e:ijk 4rz6cw.5v8 odxw)abl    W

  During a workout, the football players at State Ua ((;hqb- o77 uecs1(frtburj . ran up the stadium stairs in 66 s. Trb7jerf1;act uqu( ( 7(s-hobhe stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climbdt :q7l7( ( bu6u+f:n jdujeer 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 ou8p-rl)ez+h +;k,cs us3c,- djxkhpnfm,rb w3tput of 120 hp. How steep a hill can it climb at a h+wdb 8 mu p rp+nke;fzs,),3 -3l ,k-rjchcxsconstant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 3y7s bpdsa61g4m1 ct8whw9swj5re 6w1 10-kg box along a level floor at a speed of 1.2m/s1 w1e4817c s6b 5wjts hrwaw9g6msdpy if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.00k;hi.ddsj cs*f jkdqv75: tse4v *1 j $^{\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 buil mi7o;v3jv o/pt “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 ivov;o/ 73pj mpermanently 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*r f ad5mmsd(3tu3 gxv;wttpgd,* /d8 t 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 8d5 r ttmp/xdmdgs*3wv 3 (,*;aftgduholds 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 famoux .5wqqf(;69y 6fofw+lt (ktrow7vx cs long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.17 ywlk t6f ( 6;rwctv.x95f+( ooqfqxw m from launch point to the 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 slinn0*;ekqmgj5k ml( o g-9jgz5 ding without friction along the looped track shown in Fig. 6–39 is to rem9engkkl mnzqgg0-m 5o*( j 5j;ain 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 aircraft without his parachujf6 63 my;kr86 tckrtnte oc t k; rjm3tnk8f66y6rpening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg 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 (v5e0w2h-r fvm-,e ugbb6 fit 4Fig. 6–43)b4 tfvi- m0 g,e hvfr65be2w-u.
(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 f j2ljpo6pl-nzsz217 a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Czj1 p-znfl s2j7l2op6alculate
(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 wh9 vhd*7 )t(q2,etrw2a xjwtz wen a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California clai2 hfki: )pdn-plr ;c6/y (yfdp0q ,bavms that its lifts can move 47,000 people per hour. If the average lift carries people abouth2;y/(a 6ilpn :,ff0dqyrp ck )bv-d p 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before sn()g2 ot*io7 zmg gyl;triking the turbi;gotno*7 ym2(g z)lg ine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical nh. m-.eedu x8 a2kx6oloop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the ci8 -xoh.d2 ea mx6e.nkurcular 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 dir24t wmg-25c hktf 5cwo,f9q(jia +j bcectly into work, how high could an 82-kg maaioc2 +( t-twj4 92 bck,wfcm55 fgqjhn 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 upward an23 bumum8gvs, 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 bathroom scale,9xg jev;pz 0/4xbyh r- 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 1.0ex49x hv0- ; yjbg/zpr m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s gra9pgz o0y nrwihl;6tyw , *3e3tbs a rope, and swings out over a lake (Fig. 6–45). He re9 ethy3* l tiwzr;0,6 3ygpwnoleases 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 climb(k ( /pin:ojq79o bsmes a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feojipm osn9 beq 7((k:/at?    W

  Some electric-power companies use water to store energy. Water is pumped by ew s;7a+ 0yguhsy3mr4reversible turbine pumps from a r4;+asmug3 yh 0wy7se 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 constanoeeyy( w fjoz* h t,ol4cia04eql,55. t k is cut in half. What is the spring stiffness constant for each of the two resullc ,zywj5( oey*, el.5oao4 fqie 0h4tting springs?   k

  A 6.0-kg block is pushed 8.0 m upj*.-r-g/gcx -gn,v +ag vybrx 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 accelera(:oinlb/9l 0iles s l,te from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fricti i/l 0lb(,: lo9niselsonal losses.    s

  In a common test for cardiac function (the “s un3g6d;x .;sg) hwowftress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient 3;w;nhows)x.dg 6ufgwhen the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rockn *+ibf 9-:* 8poailsw0dk and vertically upward a distance of 500 m, what was its vel98a+bw 0kia dfn-np**:d oislocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water e p.ok;sy2 x;0 yps vv;gg )cq/uxx7*twheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricityx)ysg; ox;k.*y/v; vpqt 70ups2xcg e output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s