In what ways is the word “work” as used inmy7 )ia)j 3ien everyday language the same as that defined in physics? In what ways is it differ3)n ) eaiji7yment? Give examples of both.

Can a centripetal force evera, xvhqo6 h(;s do work on an object? Explain.

Can the normal force on ani/3c 2 (lzwdx;n( wizuh6s +vd object ever do work? Explain.

A woman swimming upstream is not maapu0j1+t ;k1s;;ah 2fl dxxnszm7s6 oving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on hes+1l ;upsn t;;7xk20xf a6damashzj1r?

Is the work done by kinetic friction forces always negative? g rd- ,jswonymvn/s(:y -zh85 [Hint: Consider what happens to the di:ywjs 5(s-nh,/rvzm-o n yg8dshes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even th6hxp6r7xa 21v z4 :ufoq .tmztough you are doing no 2rv4:z1 at6 f u7.omx6ptqz xhwork?

You have two springs that are identical except that sprin3no5fe3isnvtol8/*1 b s ;cong l is stiffer than spring5 sl*oe;nsn3ct3 oon 8 vf1/bi 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 hc-k)74t nwrf vr(/5dj.wy uynorizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest -(uj7yn vfd r kt. 45rncy/)wwat þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change wkbv4wh5o6s;y9xv5 t wso49l g hen you jump as osox6l5;s5t4g y4hw wbv99 kvhigh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with z yesg3(1d;3ml t kz8vthe same speed but with different launch angles. Which one has the highest speed on impact? Ignlmtdksvz1z(3;8gye 3 ore air resistance.

A pendulum is launched from a poin m64dicslo,8c,-a walol /.myt that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches,,solm diaw yclc68/-.omal4 , the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress themjrz1i mfs(lo/ * id5(ps.a 0b spring by pressing down with your hand an1m0/lpfmb(id5sj sz .ia *(ord 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 steel wire (Fig. 6–33).w,1rk t17klki The instructo wik ,7tlkr11kr pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitat wb-4yveyacs dcjc :(uqq5/83 ional potential energy when water at the top of a waterfall fallsdscbce-c qq: (w38y4 j au/v5y to the pool below?

Describe the energy transformations when a child hops around o+f bf:dpn4b-+k izgu.n a pogo stick.

Describe the energy transformations that take place when a skier ss+b67i9x+ r hpcvo o3mcu5al) 5rfj+a tarts skiing down a hill, but after a time +5)ohalc x+ of3 vj+7 si59rcp6 aubrmis brought to rest by striking a snowdrift.

A child on a sled (total mass mbbn)kkz+l u0+f: vy0 q) starts from rest at the top of a hill of height h and slides down. Does bk+)luvyf00b+q:nk z the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step oa)8l tw se-./eat +gkuver a fallen log in their path rather than stepping on top and jumping down on the other side. Explain.)kt tugawl+ e.a- /s8e

Two identical arrows, one with twice the speed of the other, ar6.nar*4 f vjaqe fired into a bale oarnvfj 6qa*. 4f hay. Assuming 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 swinginlh3.x lvq(/xo4a r-zeg pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clocx3/rh(lqz4ox- vl.ea k has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its ori9(orx3:9l fpu *k pntjginal height? Exn *lfkrpxp9 (u9ot 3j:plain.

Suppose you lift a suitcase from the floor to a table. The work you do on the su x)zvat1ul4p4 m -sjf)itcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the wxpzv)1)j sa-m l ut4f4eight of the suitcase?

Repeat Question 22 for t:dhb,o /)fjs+(lz p wh )ycb9dhe power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trailb: l 1f9r6n1dhjvn)s+: fq plj than to climb straight u1n:nrjl1j)fd+ 96l fv:ph bsqp?

Recall from Chapter 4, 5d wb :usnz p)5;xj3l:vu5w-q4an fomExample 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much o wluqn5vf:szbxu4 )w 3pd-j: ;m5n 5arope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile dr1l(nfophg 9yjgco;rw tq1 7f4y -e-f9iver falls tf- -lo17j4y 1pe h rqnffw;(gcg y9o92.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muchf5q5pkzh fm c8.4 ma,u work is reka5ffcm u,8h4zq p m.5quired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at cons+s2qb9tdq h:ku)o 7 i)o.4i qhvn/ qvytantt9iu qooq4hn.q)hqi7 v d2/ v+kys) b: speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-8l8bh xo+2 bj* 9- ,rgrgppekmkg crate 10.3 m across a rough floor without acceleration, if the effective coefficieno rmkj 2l-9bb,e*r p8ggh x+8pt of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor 38 z/ xhnrkjh e1vh5v0at a rate of for 7.0 s. Find the net work do r5xkhjhn08h z 13vev/ne on the box.   J

  Eight books, each 4.3 cm thick with mgoeemgy 984pa f :)l9rass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of o8a:e)yg f9eg ml p94ranother?    J

A lever such as that shown in Fig.hxhlgrn ftp7af 6j3*-/. eel- 6-35 can be used to liff objects we might not otherwh*-a /e3-pj. hlnfgfe7 ltxr6ise 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 28° inclin ,z dswpra)1z699x+nqjmw h m2e and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig.rj6p9zz 9a,1dnshqm) m +2xww 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 of ql:klp6r8 eu9 mass M an acceleration of 0.10 g u q: rpe9k6u8llpward.    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 z2 973 y*4uqg p uetcnp:1xqba/rz.xx 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 aud :30b 3,pbzgox)c5r u/ko nllong the x axis, varies as shown in Fig. 6–37. Deter0 l35n/ ug )zoxukbdpo3:c ,brmine the work done 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 particle acts9q6 rp.evtrr4qe(+i+wd1np wsj*gk - in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen moqb8vt;v (nt) ylecule, 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 factj:;el3g7- ek nm0xzppor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requiredc--alwm.b8g9 c 75f (r usaqto 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 to stop a 1250-kgcar travelinvt2 lye,seeq1o ,m.x-g at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 N a(k+f :yp5j7 hf in4*xpz* onton the arrky(n*:fa5 f*7t+nippx4h joz ow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25e x;wm ,88dz1a imtyp4 cm when the ball is caught. What was tdp,; miea w1848yzxmt he average force exerted by the ball on the glove?    N

If the speed of a car is increased.ukvq -x)dhp 7+2lfbj g azs*, by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the drivshz. d)*a lvfqgx ujk-7b2p, +er’s reaction time.

  At an accident scene on a level road, investigators measure a car’e9 ia7*ccbh jk a 51jw,;h,lfb -ab*eds skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed *ebb fw; ib j7c c5-jh,a,ah 9*ek1ladof 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 reaches the -+tonbapnt 69 plate, it may have slowed by 10%. Neglecting gravity, estimate theb -+tp6non9at 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 does 80.0 1 t i.uz1e1irqJ of work on it? Neglect air resist 1ii .t1ruqe1zance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratio21gfk 7f2mes7+aj3 r8.j rt*sdypwx vn by a single cabl mr+fx3ja.*d vpjsg1f 8s27tk2ew7r ye. 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 cons hd vv(4nk(g2etant, k, of 440N/m How much must this spring be stretched to sto((v2knh d4vg ere 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What 5app96duw.u iajkn .;is the change in potenti 5wiau.j a6kdn;pu.9p al energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chs k k9dh rm-gyq2-j44tange if his center of mass rises about 4.0 m during the jumj-4th4-kgrkmy d92 sqp?    J

  A 1200-kg car rolling on a horizpjazi3()k/ thontal 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 constanthpk3)z i(ja t/ of the spring?    N/m

  A 1.60-m tall person liftsc6x.umay0*ni+ x ipw9 a 2.10-kg book from the ground so it is 2.20 m above the ground. uc w+mix9iy a* p.x6n0What 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 elevation of 1600 m and climxb v,rksv99((qzoerh8 bjw4/ bs to the top of a 3300-m peak. 9zw 4(k o9,hqrxj (srvevbb8/
(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 ruler. The 276eboi8ij2c9hxc s iend of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with tiib c27o2 8xiej9 hs6che ruler marks?    cm

  Jane, looking for Tarzan, is running at m0/r zmfwg0b50 uh9 ixtop speed (5.3m/s) and grabs a vine hangri0xgm/z 5 f0w0mbhu9ing vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fv6bc b mm(rmp0mrh ) y4r(u2d2rom 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 givenoqxr7a 3-f*lion2bn/ a shove 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 kineti nh 8 x(0xl99k8epawqac energy is transformed into gravitational potential energy without the aid 89na0welkx9x8 p(haq 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 8 t8x, n;-izircc*wan upward from the top of a platform with a speed of 5.8,xc- z*wi;rintanc 80 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 spring stiffness constant is 950N/rplv/ f-1og6t m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball whgfvrlo/ 1-t 6pen 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 ld)e.b5* . l7gvecsvvm ooped track shown in Fig. 6–39. If the block is to remai5v sb7.leemvdcg ).*v n on the track, even at the top 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 s k o6j6o *qdc/f 3fv51ql6yhkend of a spring (spring stiffness constant k), Fig. 6–40. Toqy6sk56f fk d*h 6l3 j/vcq1ohe block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungemu3fytng0bc.) 9(km2hd g/ u te cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assumin y3b)(.9nd mug g c/2tkhtf0umg 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–sr ao.m4:9w y+-y5qr ul2e ft k;bcmb641 is dragged up to point 1 where it is released from u2m4mtra.r+5q kwbcy-6l e;y9sf b:orest. Assuming no friction, calculate 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 a8ybt dsn4 :n5jvx0y8jngle 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 elevat e+a3u/ )/dghzi+-qbfncl8gtbz 0g 2 oor 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 constant k should have so that passengers undergo an acceleratiot)e/b+0qf +zzn 82/ggcihuog b3adl- n 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+eseb hek 0h0 sv7o/7w 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each wz. -0pbuo98 kf(*xzlcx 9ujzc,bd0t of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How mxz09c*-cdbo l98 jx,t(f p 0zuwzub k.uch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wio*v57 .nul mrsth a speed of 2.2m/s How mucrosl7mu.v*n 5 h thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22j*gbk m1 t0k)b $^{\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 a :kfn1j hq)py4bove the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of iml-b7a0 bard*o: v z-1.5 m.-a:0da o7 b*bmzil -vr
(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, startingd5l:b* /yafx a from rest, is pulled across a floor with a constant horizontal force of 350 N. For the fira/f ayb*l :5xdst 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 spe z- 7 uo1iu6drhq4ylk5ed of If the av4q6k17idor uy hz5lu- erage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s re,)o (kh /( qp3vcuviif bf7-araches the foot 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 firmly attached to a very l/shg *i:hd5+ qo9fpkoc u qi7ty 47;sqight 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, stret4p;7ducsg q7q5i/t 9fs+*io ykohh: qches out 2.3 cm beyond the 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 attached to a very light horizontal spring,o9ck 9akpp4x- fr .w:g 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.cp-9:kp 9rw ox fa4gk it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg vxm369x3v 2 c:hvz 0zk (ybaz*onzj+l including pilot) thx2hv*(9 b60zz3mckyvzxzvnj +: 3a loat was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 175jnm,9 nms) utt;rh 4/o:m0nhzbn.)rb 0-W motor to lift a 315-kg piano to a sixth-story window 16. z m94nhu t)0snn/mtb b.:romn)h;, rj0 m above?    s

  If a car generates 18 hp whenv vdxjd7(;ol* traveling at a steady 88km/h what must be the average forcj 7l*vddo( x;ve exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car acceqm lnu t3yq740ajh6e)lerates from rest to 95km/h in 7.4 s. What is the average power ) en4atqqh 6jm ly03u7delivered by the engine?$\approx$    hp

  (a) Show that one British hk(d 9-;q,n4nxx 5jntp2*oms p gnruh5orsepower$ \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 e+ox5d e8eibl2: cg7,gvdc)a “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 br02lgn c. j.vq yssv)o/u)lcbb/5w .to 65km/h in about 6.0 s on the level when it is in neutral. Approximately whb)lcu)2w ./by j 0vc/nsrgo5sv.l.bqat 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 *owrq128jkybusy ,6 ikgni 6, motor 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 If this z0mqc7zln*7h7 fqnj e2su 5i+motion takes 1.5 *u fqj n5l7shi 77 zn0eq2m+czs, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hegos :s ok4h*xf413rda ight of 3.60 m. What output ratinf3asdkrh g 44:oo*s 1xg (watts) should the pump motor have?    W

  During a workout, the fus/d;ap )w41ra .ef:3chu ufz ootball players at State U. ran up the stadium stairs in 66 s. The stairs are 14;awhf3.u4uzs)de a 1:pfrc/u 0 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 climb a j2qqm+h 5qyi*fqh ,x36.0 $^{\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 it cock1m2ea +ke7:s rg4flimb at a constant speed of 75km/h if the frictional forces add up togs:k 7mc+oka2r4efe1 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dmiu.8i s9a7imrag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of s mu9i87miai. friction is 0.45?    hp

  A bicyclist coasts down a j svf;u.kmjn 46t,8of 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) 5vm ))y txz.kzbumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but 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 inkvx mz)y.5)zt to a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library ,x(pewu e+.k(hn - gsvthe first 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 holds 25 books, how much work is required to fill all the shelves, assuming the boogs+(kwp (x.ne h- evu,ks are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump 0rbo)ytno 81awgd , v9e3p/9lehkc 3p(Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was tran1/b kcg8a3tpv ryp9e o0),dw3e9l ohveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without ez./.t30 bn yfs9atbk friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even atf.. e9t/z0b3tsna kby 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 pari.lb.)wph *rw achute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wasb wl)*h. p.rwi 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 dvel)3ms ,d078cfrz/iyp0 ncid8 n, fj7.laxof length L whose other end is fixed (Fig. 6–43sdx0fcj)0y l /.azl7fpivei8r7 d3,8dcm nn,).
(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. Twzlz+ke sq/m trl )w47p+.2dqhe climb is made in 5.0 h starting at an elevation of 2300 m. Calculql7w. +pz+r)ke m/2q ws zl4tdate
(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 elev8d frwsi8zt.7 ator 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 clg+wzvm(( raq9d c/z9 aaims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate thav(gqd9+a w /z9mz(r ce power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s a+z3vj2ur uwor/x r 9clv/ i52rnd falls vertically 81 m before striking3/i uv+ rrw/2 jrzcl92rxu 5ov the turbine 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 l 60ut dy;-zmca circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the ld6 mtc0 ;y-zusize of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high couup,6 z/u2irgl yaq-;c ld an 82-kg man climb a ladder if he were fueled by one bar (lurz q-6/picag y, u2;=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 yc 0 dx b+qcy6c/i0jm+u uxe2-bin p1*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 bad .4 7*krdnavsthroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m.s4dr*an dv7k, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs4q.g s;ehn,db a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velqe .d4sb,hg ;nocity 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 ver n+x (tj*uw-tfd*zxppu *gi75 tical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplisf* u pw* zxgint*-puj7 t+d5(xh this feat?    W

  Some electric-power companies use water to stor::b l / o1nnj+mrvi*d. te- a9cjdrxl)e energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produ dn*rl: jxr:9b+e.-tdvi oml )/ancj1ced 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 c *i/aa0; *poqyefk-eh onstant k is cut in half. What is the spring stiffness consta;-f ay p*aqheeo 0k*i/nt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 w;zly+;pcmrd oh6ag1sf qyh :8439bf 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 fr)x :ibzg+(gpe om 35km/h to 55km/h in 3.2 s, how long will it take to pi:+b)z(x egg accelerate 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 “stress test”), the patient wavunl;(xu:o9-nsfw tjjlm :5*rsho 22 lks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the tre;lluh:ouns52- rx2(j:svo 9m*tn w fjadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance dx9u+/lfapj+c ++a/+d lvyr pof 500 m, what was its velocity when i9d+/+ faplr++ /apl+ycdjxuvt 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 heign6:o m ghznxl( e59s,+*fa9z)rxezwb tq65pkht of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, e9sz+xlnx z fkz eb56)*pw9or,6m t(q5ag:nhwhat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s