In what ways is the word “work” as used uuy /.70 e n.ysqce3inin everyday language the same as that defined in physics? In eu yin0 7../q yenus3cwhat ways is it different? Give examples of both.

Can a centripetal force ever do work on (x*1erp1trxi an object? Explain.

Can the normal force on an object e3y v/n8lv7rg kver do work? Explain.

A woman swimming upstream is not moving with respect to the shore. 4i9 xcj 5;lb19lzs/wdk;, n 4hnauzw uIs she doing any work? If she stops swimming an 5b ;9uc; wh,ax/zlu19jdkin w lnzs44d merely floats, is work done on her?

Is the work done by kinetic friction forces always n gd z0an-h4b*k., 2+a-tzwdojb6df qf egative? [Hint: Consider wha ndg- .a*hd0baf kz,jdtqof-2b46 z+wt happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing not8mb tg-0kj x +ilh7n7va3zs 7 wos- xbtt87m7 klh+jz vg730nairk?

You have two springs that are identical except that spring l is stiffgs :w96n z4zkser than sprzg:9z4 6swk nsing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to h ,9;n hpb66pvdk4uxjc :+cgcslide on a frictionless surface (Fig.6-30). The block starts from rest at þointc;pkb+ vc c6 46x9gu :hnhjpd, 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 potentisf kfoagz:+smr:4515sxo /we al energy change when you jump as high as you can 5s::kf e4 wox+1razofm5s/sg?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with t r;0n8*ebw djbhe same speed but wnw*80je db b;rith different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that syr+75oc wydy kv)6ps vqy5 +;is a height h above its lowest point in two differeny)+ocqrv7 6w ;dys v5+ysp yk5t 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 table. If you compresr w1 )0kyr:oups the spring by pressing down with your hand and then release it, k):1pru0 ryw ocan the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceilingys2jq)25ntpr tp-/k68 amju s by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supp2j)ja-5 yktsrsppq8u2nm /6tosed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at/enxu)(*xwkd 9 i5tzv the top of a waterfall falls to the pool belowdx xtiz9*v)n/5 uwke(?

Describe the energy transformations when a child hops around on a pogo sywxco w( qnp2+9hjdl(oy6, ,qzn) )i otick.

Describe the energy transformations that take place when ajud z8c4 t32fm skier starts skiing down a hi dfzcmu 42tj38ll, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) cjsv-ny1p2 fdi ( f-x3jy,-ybstarts 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 (b) there is friction (deex dvf2s,p cjbnj -y1yi-(3fy-p snow)?

Seasoned hikers prefer to step over og(l2o l47z:j*l x/dbpnky( c a fallen log in their path rather than stepping on top and jumping down on the other 7n(go 4lb(ko/p*y ldx2z:jl cside. Explain.

Two identical arrows, one with twice thi0gb*ve .j(ou m, yfa:(vune6e speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, them0 eau *eu( v(gif6j:n.boy,v faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energ5k(cs1w z0xi6pg ph ,ey, (a) ignoring friction, and (b) taking friction into account. Exp p60kz, h wie1xs5cpg(lain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a hk ey6g q. f,r(pr db(/1 vo+d4s:vssfheight greater than its originafqef hvsg.+bdvr4sd r s(/,y:1ok (6p l height? Explain.

Suppose you lift a suitcase from thepikd0 n: 42hlm floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicatedpd ik0:2l nm4h path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the pown4inf qo (vco ):2n:lser needed rather than the work.

Why is it easier to climb a mountain via nccq;t rj2 t/.87 nke9gmoqh1a zigzag trail than to climb straight up hqgqneo ; .8t mtj9kcnr/127c?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to decolbpe(rqhl j+a:6ql f5me9. 0rease the force needed to raise a heavy load (see Fig. 6–36e0la9 j eorl mlhq(.pf+q :5b4). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fanjssr3qw x,n 7y b950glls 2j 3 0r,sx nn7qbwg9y5s.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How +a 6ab0yn;ujd much work is required?0abjny 6 d;au+    J

  A 1300-N crate rests on the floor. How kuj:n1ya/sg9k: or y- much work is required to move it at constant speed (a) 4.0 m along the floor against a frict/y a:-ky9oj:r k1gnusion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work diq13yr, jksmngho -9ng t, *x0pd the movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?,0*oq ,9n3 jtp -ky1 nmhgxsrg    J

  A box of mass 5.0 kg is accelerated by a force i(8uvx)rh6ct a+or9)df fq lr rm5 fe7)0,pg kacross a floor at a rate of for 7.0 s. Find the net65ri+q)7drm)rl,9 xfpe( fcrvugk80ha) f ot work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat :vngyz*m +biml( 9jg (on a table. How much work is required to :j( *yl vibg(nmm zg9+stack them one on top of another?    J

A lever such as that shown ir6d+h ei:4ife n Fig. 6-35 can be used to liff objects we might noti+:d ie hf4e6r otherwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6lsjvmb- n a7i68wz6 (d m down a 28° incline and is kept from accelerating by a man who is pushi(8svb zj ld7-mnawi 66ng back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an accpxss.3vx m/gt.t:/u . mhqerlx 7pw, 1eleration of 0.10 g m.lq..svp , xg/:xwx 3tt/ephs1u r7m 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 distance axia9bxxnqg6xj js,89 w)(6gch vs 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 thy8:gav) u cgxrxlgz7; 9ap9:qe x axis, varies as shown in Fig. 6–37. Determine the work done by this force to mov yg)gvqc:99 xg8a7;ualr:zx pe 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 particl4d2d phvaee 50e 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 oxygen molecule, with ma:7 gtb8vw.;fyj 86k ic vplx/lss 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 increase r pmrgx)d m0.n.-bd5id? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to st .wv07d4 tqxk4qe).vfsrtn , f7r nx/cop 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 1257 5)nowir2 dtz0-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 n p ftz;*d hmbb2a72s*N on the arrow over a distance of 78 cm. What is the speed of the fta*b 7h* d pn2sb;zm2arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelint qk4np/ry(jb)q 0m) ng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by ther0t)qymn (pk /4n)bqj ball on the glove?    N

If the speed of a car is increas:dim1dr/)d ari9b3f a ed by 50%, by what factor will its minimum braking /:1m )bra9if3rd dadi distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’fz 6pdbx, ;q0ss skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kb0z;qsdx p6f ,inetic 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 k,xvojjy1xk yy.(bp9fv2id)gpeeu**k ) eh0 .g is pitched at By the time it reaches the plate, it may0xgphve,))e (2b*pif d . ok.vjyxk9 u ey1jy* have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrownqiuiyt)8fld/a2h,(f soa8c is .i6o( straight up by someone who does 80.0 J of work on it? suiot i oqd((f )ifs2,8ch6li8a a /.yNeglect air resistance.    m

  A 285-kg load is lifted7g5lq7sx :tgb 22.0 m vertically with an acceleration by a single cable. Dete5lbggxq 77t s:rmine
(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 conw8 xg; 84xgatystant, k, of 440N/m How much must this spring be stretched to store 25 J of pote8ytwggx; 8ax4ntial energy?    m

  A 7.0-kg monkey swings from one branch to *me7j/ds,770 jsjfp w4yjzjcanother 1.2 m higher. What is the change in potential energejfs7pjjzj/0s,4dj c w7my7*y?    J

  By how much does the gpb0: 2v zbr)ofca o+gyngu:*. ravitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jag:pr zv0yc 2fb+un:og* o.) bump?    J

  A 1200-kg car rolling on a horizontal surface 3j2s91u nfr/ nwwyl:-9 jkwep has speed v = 65 km/h when it strikes a horizontal coiled spring and n y1n:wrsp9wje 9- 32wjf/kul 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-kq5ha5-e c0 ix)cpw s2zg book from the ground so it is 2.20 m above the ground5zsx 0eqc)2piha 5w-c. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the t 2za)a6 y/nxwzop of a 3300-m peak. zxay6zwn) a/2
(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 the spr +h / mtlo.:joylkmn52ing is next to the 15-cm mark on th mly+n.:o5o/2kmt hlje ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed ( ij34xh1xl62ce .tx qp5.3m/s) and grabs a vine hanging vertically from a . q2p xet1hj46il3xxc 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 from rest, z6m qbpne),wp6.: kcdslides 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 shove up a fryi79t)3lebxg5 )f zi3b8a jx sictionless 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 transforj t0bofa fs* g4 jv;o+.mh *f)9rlw/kqmed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 f4rq *v.lgbfj;a o9s0h*t f/kwjo) +m m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwa+ef bxnvt1+)8roof)u2 jrhs /rd from the top of a platform with fsf oh+jvr)xn+/ 1b e 8o)tu2ra speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its nb ru;/cru h:6r4j .xs)x fn:5/oiez kmass), whose spring stiffness constant is 950N/m is attached to a table and is com:;6r n)fn:sxj cibx/ r./ 4u5uokehzrpressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in Fighbra 0:f8/u:di jst8c . 6–39. If the block is to remajuhf 0 :sdt r8ba/i:8cin 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 attache1aj(mxxk+rfhnf2). d7 i tn1q d to the end of a spring (spring stiffness constant k), Fig. 6–40. Thh)tqa(i k. r1fm1d+n x fx7jn2e 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 grglie-:5o(v dmx6flfk:+ a2bridge. She is tied to a bungee cord whose unstretched length is 12 m, and fafx :gki-fev (mldg2 6:+olr 5alls 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 sh .9g7ctsd. qf nwu46blown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no frictig ut9w4.q.l7dnbfsc6on, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thby/u . 23crac23mjx rnrown with 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 hy k0x3lfu, s;placed 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, calculate the value that the,kul03 hfs x;y 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 cyc-uh(8j g* fxt 79*ijcw8ve7d an)bmq2b icwg4le up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 76qxo5 ;7u ppig6wh z9t150 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal enert puh6gp9wi7 5o;q1zxgy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sligv.c s ;9+4sim+kxd+i c/tk ssde 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated i.ssskv9i+ timkx/4+ ;sd cg+cn this process?    J

  A ski starts from rest and slides do dr:2)yfga7dgwn 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 g4fxsr is,* zu8round.
(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 1, ,hrkqj8if zke g:)slx.vl *(.5 m. 8,r,(l:. q ishgfkz) ljk evx*
(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 pulled ac/ c,m9gzx*uzfvia9 3g ross a floor with a constant horizontal force of 350 N. For the firs*gmua/v fxig9 3z,zc9t 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 the .a2l lpd-s o7c; bk7mzaverage force of fric-op7db2 lc7.lkz sm; ation 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 on :,y aatw+u6 3e0wyhy ux28hlf 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 firmlye b7+kur0fib; attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and tekr 0bbf; +u7iurning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attac+ m-kmfh y2jx92ro k3yhed to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its+o ry92x 3mmy-j kf2kh first swing?    m

  Early test flights forg qulmls7 /p7) the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. Tq 7u) g/lmlps7he glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a g/ mhknfm-y8t(:w(xec(w m0vsixth-story window 16.0 /vtm( m-(h(wec : 8yk wnf0gmxm above?    s

  If a car generates 18 h+fv h9s d w7klbv(8uax*t;ku0p when traveling at a steady 88km/h what must be the average force exerted ondk0lv+;hsw t7 xvu8fu9 kab*( the car due to friction and air resistance?    N

  A 1400-kg sports car accelek;s r-8 j570g w: uhhuvo)pjvtrates from rest to 95km/h in 7.4 s. What is the average powekhu hpv-7ortj :ju ;08g)w5 vsr delivered by the engine?$\approx$    hp

  (a) Show that one British hoinl fc*dme/bm ,tu0z h*t-3 :srsepower$ \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 expressedxuhp s4,*9 noj 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 to 65km/h in about 6iqv7v 985-p *jjcrnqg.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75 7*jrgijpv58q9-qn c vkm/h.    hp

  How much work can a 3.0-hp motorw p mcsbztz6 .zm738 07lx9y9yy l-sry 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 t)fy0 k1sy f+fIf this motion takes 1.5 s, what average power was de s)1 tf0yf+kyfveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What o h(o ic5l2xr+rutput rating (watts) should 5rrih+x(o c 2lthe pump motor have?    W

  During a workout, the fo*ym mtgods3k, 2)u jl1otball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long 2y,13s)o lkdmtujg*mand 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 6.0- twrq2wbq ,dp5o(j*w $^{\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 cz*a+fw 7/(g yf lofoc dxg/42wlimb at /f4wzlya gw(ff7 g/co+od2x* a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have toxqngcyw ; 9jid2 mw013 be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictiiy0dn 9cx;q wwmjg231 on is 0.45?    hp

  A bicyclist coasts dow9oir8y ;. gut2rwj4eln a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s carcg0i ,mz .zss:s have built “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 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, assumz g. scszim,:0ing 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 the ground, and the n1dtw(wch+ mc. p9ou+ v (dfp/remaining four shelves are each spaced 30.0 cm above the previous one. If the averao u c+c(dfdm9p+hwp1 vw(tn./ge 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 fam (pl 0ko+k:*gv:wlspsous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch pg0+:ko p(vwp lsk s:l*oint 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 without friction along the loope w21ou+f -ajc93dpek kd track shown in Fig. 6–3c3e19 +ko2kj afd wu-p9 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 37t7 6z6++c og6jaf 1xljky,at e0 m after jumping 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. Assumingxj 6t+6kfa,7z6ej1agt +yl oc 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 isjb naw 4w87mq6 fixed (Fig. 6–43jm74wwn ab68q ).
(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-hicutu .lxf 3;2zgh mountain. The climb is made in 5.0 h starting at azuc2; tf.xl3u n elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevatorz3av p*0a 2 aj hr x08/lsn,9jis1z1zar3gy pm 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 ares *b4x459f gix79qz i xup/jcia in California claims that its lifts can move 47,000 people per hour. Iq9izigipfbx7us cx45 x49j/ *f the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 65o(mkn(h5k3u n: vt2 jqg bgz)1qjx(i ,0kg/s and falls vertically 81 m before striking the turbine blades. Calc:h ngx)jjn( omkz u tq1vig2 ,(3(5qkbulate
(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 wq h-c6/ 0zpc-h 8jibofith a 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 size of the loop or how fast you go through p6-fc-o bzcih8h /jq 0it.    mg

  (a) If the human body could convert a candy bar directly into work, how highe(yyk8(li+aj :b/ k vx could vaek lj(8yxb:/(i +kyan 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45 6e.nd;gl thd4.0$^{\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 bathroo 1y.c6.h nrdhem scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 1ynd ehc .h.6rN. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and sw ftzh 9pa37ai g8,n+tw* ;qbhnings out over a lake (Fig. 6–45). He releases the rope when his velocity hft t*g 9zaq+7nn3w;abi, 8phis 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 atdmlsw(8w/0ecr 7os /thlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to alo ms r/s /7w0w(tedc8ccomplish this feat?    W

  Some electric-power companies use water to stor s8fs 0azy bv,41ztj suuw0l.+87safx fgy q;+e energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 8sy;0+sfw.gly018,s+ qsfbvf z7zjax auu t 41.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spb jgw8*d6:ja g4ix* dvring stifg dv8ijw* x:*jd 4gab6fness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up ai9tu,xivctkv*i (70zl u;a,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/h in 3.2 s, how long will ito s bn,2h67ciu5 +q:dmae1ven take to accelerate from 55km/h to 75km/h Assume the power stays the same, and ne5n ndvb6a:21+, ohce7 suqie mglect frictional losses.    s

  In a common test for cardiac funloxce7kq s, h. f5vb:)ction (the “stress test”), the patient walks on a5o ch,kfq 7 v.sl:)exbn inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanced j1ucld9.lv 7 of 500 m, whatd7u.jl91v d cl was its velocity 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 wheel from a height of 2.0 m at :sh4k 93 pc vnx5*zkgsa rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power g :pk59zc3xsvs* k h4noutput?    W
(b) What is the speed of the water as it hits the wheel?    m/s