In what ways is the word “work” ad;j6fp+s r,ma s used in everyday language the same as that defined in physics? In what ways irj;fs damp ,+6s it different? Give examples of both.

Can a centripetal force ever do work 1)ru0 -nxf t tru,*t vo5iuw :4ni+vqjon an object? Explain.

Can the normal force on an object ever do work-lz c,r7(zp-1mbjfe v? Explain.

A woman swimming upstream is not moving witht uwo vywp 9p(,j 3ye.gg;0d9v respect to the shore. Is she doing any work? If she stops swimming and merely floats, i .p 0uvjygwe(w3,;tg vyo99dps work done on her?

Is the work done by kinetic friction forces always negative? [H l)eq.,(*oc1dhjww ri-jz i2yint: Consider what happens to the dishes when you pull a tab-iryjo(cjd.i2elqh 1 w ) *wz,lecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doiei:t:etav+wpif/ n7 xskt6m/u+r-. p ng no wo7xfuv ti6: ak+//e-mett+p i. srn:pw rk?

You have two springs that are identica*uo0w 7ke/rohopzhq 1c;y9k 2ens-u5l except that spring l is stiffer than spring qp21er507ze* ; 9- yowohoukcsnuk/h 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 constant2-* ( s:0qw ozfzjza)l1xj mic horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest atjm zo02acwf) jqsx1z(i- *l:z 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 gravitatioxy)hi(ih 6m, y,r aonyb5*n.unal potential energy change when you jurhy)*b , n,i.ha xo5niyym(u6mp as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a bua9ne7*9uyzinj0y61h ll1m uuilding, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignou1u9hyy n a091* ll6im uj7znere air resistance.

A pendulum is launched fey( +1dj4i)lstz (cd 8 zgh*vwrom a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch+de)it jdg z8 *1syzlv((w4 ch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests uprighth jo0/0*at.ib (cf su vs.x5ml on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Expll js0(/f m *b5.isao.0c tvxhuain, using the law of conservation of energy.

A bowling ball is hung fro gqni.oft(:kfw+ 7 7owm the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball bacgow.(n q fi7k+ wf:to7k 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 gravitational potential energy when pxqh3 udt6t ,6glr;v/-mkw7cwater at the top of a waterfall falls to t6/lgqm 7- kchx,6rd pt 3u;wtvhe pool below?

Describe the energy tray254bh tnst f;*2uk xcnfk35 snsformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiibke sae+us-vs6 i e;3/ng down a hill, but after a time is brought to3 ibeu;6/ asves- ks+e rest by striking a snowdrift.

A child on a sled (total mass m) /7 p0 jw:wxroustarts from rest 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 no friction, and (pxorj :7u0w /wb) there is friction (deep snow)?

Seasoned hikers prefer to step over a falljpun(e sfy3rf9./ *al en log in their path rather than stepping on top and jumping down on the other side. Explairjnu3es9a /*lfpf .y( n.

Two identical arrows, one wshoappm2 ev 1yn2a .k j7-e13hith twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? shy nka1o vemj-3pae 2.7ph12Explain.

Analyze the motion of a simple swinging pendulum in terms of enerdidbwbe 2-tj;yq, 13t gy, (a) ignoring friction, and (b) taking friction into account. Ex-e dytt2db;q3i1j,bw plain why a grandfather clock has to be wound up.

When a “superball” is d)cin a,3 yh ugve/9k9 zexg5g:mc*(raropped, can it rebound to a height greater than its original heighm,h vz5g* g i aye9cce9:xka/()r3gunt? Explain.

Suppose you lift a suitcase from the floor to a table. The work ysie e t1pf60zl*d1w5hou do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the phze1twls f6 *id e105weight of the suitcase?

Repeat Question 22 for the power needed rkzcc;8dyfguw p63j l6 rl,3a/ ather than the work.

Why is it easier to climb a mountain vio)xm vkmq2 fx+a bjh3, 7l4y ym9t8b:la a zigzag trail than to climb straight upmal lj )xy2o myt mhv87xq b:kfb3+49,?

Recall from Chapter 4, Example 4–14, thafu +9g5t flo inl3q8.ct you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But f+ilq uf9fgo.3 8lct n5or 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 * c 3myvlvk/:7is3pgdforce when a 265-kg pile driver falls 2.80 ms3mv gd:kc7vpi*/3 yl?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How mucrno; n*ss ocqtp 9yox+87at8,h work is re*o,pyn88 sn+;raqcot9x 7tos quired?    J

  A 1300-N crate rests on the floor. How much work is requ s u04iyzhxsu1zo)-89 8 dd j;rtwc8jvired to move it at constant speed (a) 4.0 m along the floor against a xdu)vijdsz19zr-sh4 88y ;utjw8o0c friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movera.(m6 zo6z+vcp.scdutfjj8(s do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of fasz+oz6p. . f8ctu ((jjc6vdm riction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a lix pm1;l n0;brate of for 7.0 s. Find the net 1i 0;xm;pblln work done on the box.   J

  Eight books, each 4.*ua)r* pieu h(bb6l l83 cm thick with mass 1.7 kg, lie flat on a table. How much w*hpl( 6e)arul8ib b u*ork is required to stack them one on top of another?    J

A lever such as that shown in Fig.xtwrxr89k)v5.juu/l 6-35 can be used to liff objects we might not otherwise be able to liff. Show v)9wx58xu tk/lr jru. that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and isic r9,cc k19cfa0skg 7.dnjw : kept from accelerating by a man who is pushing back r dj9ci .,wc0kas cgc 9k7:nf1on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter oy1 b8awbw3vt.f mass M an acceleration of 0.10 yvt3bbww18 .ag upward.    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 dista40kh6 y o;up;f x8ycbence axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, actinm f80.tq8ttf,- hczp kg along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) p tcz0h,f8t 8fqt-mk.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 pa0u u 1o/7vjwrurticle 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, anz/n7vy pk/(k y oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed inc i)es2bl1u3ny09fyu o reased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requiredjc6:ggy. s bf7fj +plt);m 1ml 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 traveliy :* a3z v;r8nulie0xpng at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string hof.l aa1k7ywus*dlw+p h30* exerts an average force of 110 N on the arrow over a distance of 78l3 lksh +pu*7h0wwfa.d o*1ya 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 glo5.xd5- -vg7q8bn qf *sf3vessy q p2g)kb z*uove backward 25 cm when the ball is caught. What was the average fo*v*.u7 o5n5yg kzqf v2-bqs-s 3gp)qs b8fe xdrce exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what facto621zu1p hn*yfpb:. tzw;f nn xr will its minimum braking distance be increased, assuming uzn:;ppxy 1zfn b*6w.h2 ftn1 all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s ski,eyg . )gvyc)enh8wy. d 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 o8 .y eg).ygn,w ch)eyvn (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 reach:8k w6+ap f 99i6r:cf ennnnwbes the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the platebr9awn+6pinen9f6 n :f wck :8 and the pitcher is about 15 m.    N

  How high will a 1.85-kosyh+p yeo7ad g j zk-+01a,m t0do-1ig rock go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistance.t -70pzoi1o,aayeg s k+ -dd1hmj0yo+    m

  A 285-kg load is lifted 22.0 m vertically with an accel1eosvx gn()g)eration by a single cable. Deter)(ge x)v nsg1omine
(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,nr02at +fl5ibz7(ty lax. ua. of 440N/m How much must this spring be stretched to s. la 0i.l(t azy7a2 t+x5rnubftore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher.52wzh l+xt v )s+tcj6i What is the change in p52w + tsjcih+xz)6ltvotential energy?    J

  By how much does the gravitational potential energt+ rmecz(:b* ty of a 64-kg pole vaulter change if his center of mass r+te*c b :tmzr(ises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kyf1qqwj * -om:m/h when it strikes a horizontfq:1w qoyj -*mal coiled 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 from the ground so it is 2.20 m abx :;jhcsl0qg2 r,p5giove the ground. What is the px;qgch5g: rsli,0 jp2 otential 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 elevationu)4)bm7jcn rwwi5 .s ub tn,4if 4vd.k of 1600 m and climbs to the top of a 3300-m peak.drvn n.)j54sf4ub.imu k)w ,7ib tc4 w
(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 end of theci r2 kvduk6r-1m ;0hv 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 the ruvkum v1h -d6;ik2rr0cler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and glv0u+4 tve.oj rabs a vine hanging vertically from a talltj0u+v .eol v4 tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dqq,k am)qg;)jnkmyq,tyj e4 0as3 4 *pown 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 b nf c 8if8mx/o.ptdubg, s qoz .d;z(zvr-)7;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 kinetic energy is transformed into gravitational pot: ( z7n1qyb2 io8nvvexential energy without the aid of a pole. Wivbyz:1 2n7o(nei8x qvth 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 a61ag9u) 9s hes2gzojgrtist jumps vertically upward from the top of a platform with a 6j1osasg 2 uzgeh) 9g9speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spzqb(d1f4 1gfwn 8svy/s yd( y3ring stiffness constant is 950N/m is attached to a table and is compnqg4 /z(1sy(bvsffyy 81w d 3dressed 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 loopa ux43vdq0/uz kdt5i5ed track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), fr/ud4au 530vzki x 5tqdom what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (zh1nmy8jfcp, ud6f,mx(hwj:h x,p- 0 spring stiffness constant k), Fig. 6–40. Th,hw8 1 jcxxm(mdhpf6: nzjy- 0,,fh upe 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 bunge 6y3zyi d()rqge cord whose unstretched length is 12 myrqid 6zg y)3(, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 im8rmso; xt6 4a u-1dd63s 9gqle/fvx ys dragged up to point 1 where it is ref- /orxtd6 6ya lg3e419mx;qm8ssvdu leased 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 with a speed of 12 m/s at an angle of 3;p4vxy jx s4u83 $^{\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 8gc +7o.:5pc7*xetityrhe myplaced at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, ry7e t7 :m8htpx i o*c5ey+gc.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.: b76sys,n6n n yi/njs8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite dirnnzd z9v 7-o-pections, collide head-on and come d7zzovp- n n9-to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends sqy7sl69g .hza slide 3.5 m high and reaches the bottom with a speed ofs96 shyzlgq 7. 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides dowi p a ;;byn (2ekim:f-n;pv7whn 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.l-4t/awg :e7rd9rx,8qxovor o;csr +
(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 hei0gh qres *9:q,hc uz6ight of 2.0 m, and it bounces back to a height of 1.5 m. ugs qzi ec ,q0hr:9h6*
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is puqfld ub: 2x+8,il9qk3s-vxot lled across a floor with a constant horizontal force of 350 N. For the fi+xt:8sk -9uo3v 2bq idxlqlf, rst 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 poqr ,(jm6 2hqghint 1 with a speed of If the average force jgr62 qq hmh,(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 reaches the foot of ;p.-c/tpy)mi 42 vk,ok 1 f f1znoqyrfa 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 veryo7i ev pl.ehz, ucl485 light horizontal spring (k=180N/m) ascvieo,7e 85l ph 4ulz. shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block islh6 ts -ph(i31sc67izn msvs * firmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where thliph ms3 t6-c1* vzi7(sssh6n e 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 used a “glide*q3f67 1cuqyis ny5wb r” (mass of 980 kg including pilot) thatqfuybc*6 1 5iq7yw n3s was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W mopr5/30y.2 pz5 c.ozrzebc csotor to lift a 315-kg piano to a sixth-story window 16.0 m abr02 zpzs. p 5rcyce.oc3zb/o5ove?    s

  If a car generates 18 hp / b50dcwd3qrxwhen traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resistanr 0d/xcwd3qb 5ce?    N

  A 1400-kg sports car accelerates from rest to 95km/h in yw w.,detn.sct 72mi)c :h)jv7.4 s. What is the averag. w. dven7t c,iym2) j)twcsh:e power delivered by the engine?$\approx$    hp

  (a) Show that one British vuj*j o( :sqx y7b0fqm9da0s /xnfk/7horsepower$ \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-8cg0u8d 5nhc jg;m 4shhours.”
(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 *othkf:3s rf92xu l7r to 65km/h in about 6.0 s on the lev9 f rrlhxos7u3 kft*:2el 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+e 7xbgmjuj+4 motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg -p :6 mcf rum1,fy7rqushot from rest to 14m/s If this motion takes 1.5 s, what average powmr,6 p17mcrfq:f -uyuer was developed?$\approx$    W

  A pump is to lift 18.0 kg of water pepdy9k4rijs 0 h39idh7r minute through a height of 3.60 m. What output rating (watts) should the pump motor have? jhdi3h k40 y7r9d9psi    W

  During a workout, the football player:ovs( .moiov9 jty 2)fs at State U. ran up the stadium stairs in 66 s. The staivof29t(ov :.i y)josmrs 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 climb k7eeur807j-u2;d mas t pzln6a 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 1,)d.aa6g mishn z4sc(20 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictionals6a ch4a.) gz (,isndm forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ithh: wf-h1r la99jn:*r4/y lic mx.hable to drag a 310-kg box along a level floor at a speed o ihxr:f9c4wl -iah *hr:lh.j m n1yt/9f 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 apah r2bvp 5mm r6pz44ae- ()b27vypooth l 57$^{\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) bum(q rr:iixky,zq1;sk d o(j60*6teplzpers” 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 effectiv0ls yojpz6q6* :(d;re iirqt1 x,( kkze spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off 0 *09 z3-ay e j9vmv,c-xcnay j m7jdfa/hw3vbthe ground, and the remaining four-0mz3cymwx fd,*-aa0jcyva jb97vh/ 3nv 9je 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 books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fis3kjm( zml1j a)s yzd6./rsl8 g. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m mk(8 sz/d6z 3jm slr jasly)1.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 sliding wi3z(5myaqkzm 5 thout friction along the looped track shown in Fig.m3 zq ma55zk(y 6–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumpin/ yyr ,qvky,/rw v 0ireq)u/-ag from an aircraft without his parachute opening. 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 ),/-va0iqe,u qrwky ryry /v/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 lengzwf; m8pln* +kth L whose other end is fixed (Fig. 6zl mp; *wkfn8+–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountaot v0): qpteg07 n+1zuh*rrzm in. The climb is made in 5.0 h starting:7up+ t*mze)z tv01ng 0hrroq at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 9s ix)l hr7oc)s4n. .bp20-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 claims /:tsx; kta9whthat its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate thesak;th w9 :/tx power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the i: b suzp46 ,d0vu+sqwrate of 650kg/s and falls vertically 81 m before striking the turbine bvb+dzuu4 w 6ss:iqp,0lades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical l md/se(furbcr5oks98 enp ;+)ptm5- p oop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the botto mp89c/ ;(+pu5obt-kfnpe sme5dr ) srm 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 directly into work, ho3e. wjq3o0 aaow high could an 82-kg man climb a ladder if he were fq0a3j ewoao 3.ueled 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 upwasdv+p 5m k+*turd 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 ba yahhk7vul tss e0*852throom 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 75hl*uyveas0 ths8k 2a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5iow1 rr;ek9ok-pi19 jsyu49um/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the ros ii9-oje99 wo1kur;ykp14 rupe 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 climbs a vertical distance of 5.0 m in y5hog z)i37ar 9.0 s. What my z7hiagr)3o 5inimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water,umh8 m;)qn sic 3)bm6yusi/b is pumped by reversible turbine pumps from a lm)h/msumqc )i yi6 , sub3b;n8ow 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 ha67)dw jmlox(8fw qmyt qkl,las+8 )5slf. What is the spring stiffness constant for each of the two r8 lqs)tawd m+fy,x 5s(q87wjo) lm6klesulting springs?   k

  A 6.0-kg block is pushed 8( ysf li59 by1/ooh88ijr(h sw.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 from 35km/h to 55km/hg/607lky gakr0jn) i a in 3.2 s, how long will it take to accelekakjgn r00/gay6 7li) rate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac fu0 m t7re2tn)t)kitg+rnction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). t+t rte2timrk ng0) 7)Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kgm0r* ,ytq/ap.ivt1vz rock vertically upward a distance of 500 m, what was its velocity when m0.r,1 qp*azv/ytvitit 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 whee u /rdfr7/lo9il from a height of 2.0 m at a rate of 95kg/s (a) If this water w /9oi/uflrrd7 heel 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