In what ways is the word “work” as used in everyday languagel:( cx nmrr4*1 vwze6c the same as that defined in physics? In what ways il 41v6r wncmc(z:xre*s it different? Give examples of both.

Can a centripetal force ever do work on an objec1,7p2uhl+fgwhx xxv 4t? Explain.

Can the normal force on an object ever do / v0 wtqkax) wz9-;jkywork? Explain.

A woman swimming upstream is not moving with respect to the shore. Is kn4: yc8;ffnvshe doing any work? If she stops swimming and merely floats, is wk cv:ynf;4fn8ork done on her?

Is the work done by kinetic friction forces always negative? [Hint: kg /(8n cul81bkcue;ommz+ jsxh3t17Consider what happens to the dishes when you pull a tablecloth out fro7n88 gls hm3otk ( xuc z/;kj+u1bc1mem under them.]

Why is it tiring to push hard against a solid wall even though you are dos bpzz-se9dw 73 m4r/ying no workd79 esmz3/ y4rw bpsz-?

You have two springs that are identlqy5,sy-rr5(: mfeaud72 ) za1oh j ubical except that spring l is stiffer than spr1u,bysa2 -: ()r5lqzyje5 adou mh7fr ing 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 sl prd8i0xnord 6bs+j29ide on a frictionless surface (Fig.6-30). The block starts from rest at þointj on0 prxsbr 8962i+dd 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 gravitationmn5( b svaewh9 nx +(lo//m/(/upbfysal potential energy change when you jump as high(/a(ywvof9sbbpmmu sx5l /h(/n/ +e n as you can?

In Fig. 6–31, water balloons 7u ,lqnznc1f r9y0,y7jf4iwp are tossed from the roof of a building, all with the same speed but with different launch angles. Whicn0c17zfn, ,jy 94yifrqwpul7 h one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heigqf*e (u0;hxqqxtfe-3+e0n uqkhe - c ,ht 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 will cause it to swing the largest angle frn q 3kf(q0u -eqxefc+,e*q0th x e-;uhom the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compresstyo; e3tr 9)* rnyt7ei the spring by pressing down* tr 3;eoyr7ny )t9iet with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33)./tyz7)og, w uu :byp-y The instructor 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 wit,7yu-ybt)/ :oywg zuphout pushing it. Why?

What happens to the gravitational potential enerqqix1kti)/ cyb;.1/t. i x5- wbgu qjvgy when water at the top of a waterfall falls tq1i5ig buq c1w ;bqtktvi y -././j)xxo the pool below?

Describe the energy transformations when a childgvl1u0zr*y4.o 4 ydd r9mtp2l hops around on a pogo stick.

Describe the energy transforma ueozu( w7csfx-a kza3di5(/v* p .2yitions that take place when a skier starts skiing down a hill, but kxoc 3i(uzuz. s*/-we2piy(5vf aa7d after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest abvj2:l mlwu2qo4c -1vt the top of a hill of height h and slides down. Does the velocity at the bottom dep ju: b4-cwqv212l omlvend 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 s2 x/wxg-. jzfntep over a fallen log in their path rather than steppix2x.-f/nzwjg ng on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed dlm.5i4d7p*6hc 3 ytx:rtcv jof 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 vpx my 6t3 7ic:h5jdt*dcrl 4.farther than the slower arrow? Explain.

Analyze the motion of a simprl 2 dj/b;de//vm7vaps -t7wjle swinging pendulum in terms of energy, (a) ignoring friction, lsjvb/2;vwmt/d7re-a/ d 7jp and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heighk:p- 8b.r.xz t ea4qibhoaf4.t greater than its origin 4-k4ibbt .oaahz .e:pxqr 8f.al height? Explain.

Suppose you lift a suitcase from the floor to a table. The (l4c+ad68ej -/rmzu +s gmtmth n0q(u work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b)8a m+-qdmet zus4n 0u/thl(m+cr gj(6 the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the work:lfhuh1t y1/v1; i8guc)duci.

Why is it easier to climb a mountain v7t8 flr, o) (smpc7dzkia a zigzag trail than to climb straight updsm(c7, )pz 7or ltk8f?

Recall from Chapter 4, Example 4–14, that you can usl*-ld6kp0 e6fpy sh;xm k90 hre a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). Bu9ym*-lf6 kl6peh k 0;0 rdpsxht 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 gra(jyp6vp f9+j0lgnk 0nvitational force when a 265-kg pile driver falls p09fvn+0( npj l kgy6j2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stair,p yjh )x5mnieu,.i p(cej m2z.n2l.ks 20.0 m high. How much work is required?mnj,)ii x2.(hy5,u. 2j ep.mez lknpc    J

  A 1300-N crate rests on the flo+p: zxw3hf3fkf2ay3 ror. How much work is required to move it at constant speed (a) 4.0 m along the floor against +wf32 3k 3hafzy:fprxa friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3 y1iwv0 eq0wh ow3* .gam across a roug3eohywaq 0w1gv 0*w.ih floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a f akyi7g 7)rvohed(a3.*a ojyb3.mk:iloor at a rate of for 7.0 s. Find the net work done oni)3ab7 j3:akmev(h.gr 7 .y i*kyodao the box.   J

  Eight books, each 4.3 cm thick wit,0(bibqtfe :nezj152- 6rq6ui m db oxk tab+6h mass 1.7 kg, lie flat on a table. How much work is requ5 2tq iu (-n0x+q6eb t oz:af1keimjrd6,bb 6bired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obj f6c iz8nkpm.u ,.6xtiects we might not otherwise be able .f t6ixc6.kn8mz,iu pto 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 10o voj89 w;c:gjwad vmv0ps:down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline0wdv 9vj:c:0sov8;j wpag1 om (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 Mnhjx9/c+: j*vwhaw y j,e5tg 9 an acceleration of 0.10 g upward. gjj+9nyj cheth5v9,/w*w ax:    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 line7dc 62.v3 mnvyik5sd;18v kws )psm0op,pdalar 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 aq 0fk ru y)4whuc)hv),long the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m uy) hfwkvh4 qu),)r c0to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a partic)whmr),n 5s*u,m y eqmle 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,6:m4x) ggg+ m pq8 wgc6pztwd4 an 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 tj a04-h ; tmdcnp3.:qxowiv.increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required tg1jh6hb 8w6 lqo 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 651np ww8pf1ycgyq3sdone to stop a 1250-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 1/jz5e dbkl(8; p+ d6dlf+ guso10 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the j6fsk/d;dbelg+u(ldz5 + o8 pbow?    m/s

  A baseball (m=140kg) traveling 32m/s moves y9zdjcv(yq pf xck0u43i: 8t) sg((sga fielder’s glove backward 25 cm when the b4s93)y0jqsz(g: i pct f( d( gkv8xuycall is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50xbgy)*j (yvv,2szmc 0%, by what factor will its minimum braking distance be increased, assum*y mcy) b,(jgxv2vs0zing all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investiga tdc:9u: yv( o5a1dnvutors measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estauv 9u : o:1dycdn(v5timated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches -bou5ut1mgo 1the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate a1o ub1o-5umtgnd the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if throp4twp sm*/d:p wn straight up by someone who does 80.0 J of work onwmp:p d*st /4p it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cabaou il)b+; .8 f;rgajble. Deterf)bua8abgo.; +ir lj;mine
(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, ktx0k6tnpy..ve rv 3cup//) aj, of 440N/m How much must this spring be stretched to store 25 J pra6ve /.t/ukcj 0p. )ytnxv 3of potential energy?    m

  A 7.0-kg monkey swings from one branch to anot4r iz+)o h. i5jjnu;rther 1.2 m higher. What is the change in pot.n)ojith+ zrj4ru i5; ential energy?    J

  By how much does the gravitational potential energy of a 64-kg jjxs9j4mtfaq5(6 w j( pole vaulter change if his center of mass rises about 4.0 m during the jump? jxs m t4(q6jfj(a j5w9   J

  A 1200-kg car rolling on a horizontalrqgguj0 2jn*9gvm -y : surface has speed v = 65 km/h when it strikes a horizontal coiled spring and i yjvg2ujg* ngm90r-:qs 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 oe kjv b( z.)*xz. zjrdd)2*xlground so it is 2.20 m above the ground. What is the potential energy of the book relative toz z*)(k*xx2vjlod)ze r. . jbd
(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 anqmn nw;hi s/ -vro15unm :3:vo-dqpb0 elevation of 1600 m and climbs to the top of a 3300-m pe h 3;n 51omv/indpqmbr-0 w- s:u:vnoqak.
(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 hangskcpo6,;w hh s p(/v66hqr cv/s vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. 66cp/v; h6s/(h ,prwos hvck qIf 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 s2y u4pweu4)ku peed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swinu ukw 42uep)y4g upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides d/b3,g hok4 tqoown 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 en z2c0fd*, 1-fuim thfrictionless 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 poten.b,+52geed1 gxczyg46md s;t9 dsdch tial energy without the aid of a pole. With what minimum speed must Fran leave the ground in odtmdh9xdgsg s ez46+; bec52d1 y,.cgrder 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 verti ed+wzudrh2)r 4-b/k qin;k4bcally upward from the top of a platform with a speed of 5.0 m/kd-uh bi b2e 4wd4+ zk/nrr);qs. ($\alpha)$ 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 sprlyo, jex+ z/-xing stiffness constant is 950N/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 when relea+x jly/, z-eoxsed?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withyhnvmh;moe9sz2x56o . u0it1out friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius vhizs 95h 6t2uomo0xy .1n;em is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a sprin e.)lj11ohxu ei--jbgg (spring stiffness constant k), F1 eelj-u) -.ioxb1hgjig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. S/mwnudg**fw 0 he is tied to a bungee cord whose unstretched length is 12 m, and falls a total ofm*dg*f/n0 w uw 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dxv9wnr 7p29v*9b9 zqsvdik (wragged up to point 1 where it is released from rest. Assuming no frictiosdkbr*v v (wzi729p wv99n9qx n, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a hti8gbu synneb; 88*2 /:ui njspeed 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 pl6cs lal;uh/u9up )ql* aced 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 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 ths9ql6u; lu *)/hcaupl e elevator and passengers.

  A cyclist intends to c*b )tdb3 jckt/v-h 63bn,kr cyycle 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 7650 kg and traveling 95km/h in opposite direcg rhkl, w9q/*ftions, collide head-on and come to rest. How much thermal energy is produced in th,hk/ gwqfl*9 ris collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reac94u8n ts: icpyhes the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in thiypu98:i c st4ns process?    J

  A ski starts from rest and spex-1-mog 0mfxip8u 6 lides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dro71 z)oaii o18(yfcjic c*r 7evpped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bnl 0,lo1bkvomy9 og4m1 4b jl.ounces back to a height of 1.5 m.kb,jllo44 bo1. vg1m9n0yom l
(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 across 1g:qeys p,x. ma floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of mexypg1.,q s :friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poi p9: + qgr6zre)s-nlpmnt 1 with a speed of If the average force of friction is equal to one-f n) q:-m9+prselzgr p6ifth 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 tht xe*: df2o/bde 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 light horib yzmrut)c8**zontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the ta zrb8cy)m*ut*ble?   

  A 280-g wood block is firmly attached to a very light horizontal sprie / 4qzvnv(lqy m8k lhmw14/:mng, 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 hwmq v/41v/lk e n:mzm8qy (l4on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass ,n(q; w gnhm, r0c0buvi6v*twof 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What *ruih ,60, bw; (0vwtnmqngvcwould 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 sixth-story wid4aw-7it1ln l ndow 16.0 m abovewl 74- dnla1ti?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the avdt bsn7tmm uu+;;vf(5b8( pqjerage force exerted on tb sbu;pv7 n j;q( u(5+t8mmdfthe car due to friction and air resistance?    N

  A 1400-kg sports car accelerate:do8h q(;0iz gzk d/bts from rest to 95km/h in 7.4 s. What is the average power delive0it/qb8 hd;:zdz( kog red by the engine?$\approx$    hp

  (a) Show that one British hor zlxn;cky1gl,32a gr v/f-fr; /bug8lsepower$ \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 ek9vkvr 4z1 bd/3:jujx-vh/wtitz./ 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 d-himf7 a: l4b(.yry 9h.nyfhjown from to 65km/h in about 6.0 s on the levelf.y h7jnm yh-f.r: l4by(ih9a when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dogg;la6sf ts)).l 6wx s 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 motion takes npae+j x)-vhz/bh;p; .o hn p01.5 s, what average power was develon 0 .-);x/opjh;zpvhan phb+eped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute thr/sxm2 h3h6pckough a height of 3.60 m. What output rating (whms kx2c h36p/atts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium( z0twvo3/ it0 .fezyg stairs in 66 s. The stairs are 140 m long and inclined at an angli3ov(t tzzw.e g/0fy 0e 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 cycli ti.7 .4ntmcvyst climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power 0fm+8( 8zfin *sir6jus f7mx9e o.vm,qu.lb ioutput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add uuie7bsfri6fs(l98o .xj u 0v*n,. zm8+ i mmfqp to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to uxk85 6dm.dc)p nh5undrag a 310-kg box along a lc kx.dnuhp56) ud58mn evel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.k;36v ojlp/fw fi to0;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) bumpers” thatplwpai/)n nu;2z/ p.o 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 nwn .o/2l a;u)p /ippzcar 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 gkm s)c+ (w -l+ kd6 m7nk5l4jdupla/hkround, 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 bookslmd m6kwl khjul74/(nscdkk-+)p a+5 are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) inbopr+ 28:wawt 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 travwtp +w 8o2:arbeling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopygs;3z w hsi(lc- q5*v3 tf8z4 ary2pved track shown in Fig. 6–39 is to remain on the trapqag3-r lzy35wss t2 vh;*8 vc4fi yz(ck 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 jumpiwj et 0+g,ut9i9hw xy-ng from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor 9twjh9+ 0tg- uy,xeiw injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizp4cur8ljq p,/8)l1 w8n uaq hlontal cord of length L whose other end is fixed (Fiqpqc)n8ulwa8l/ r 84 ,jh lpu1g. 6–43).
(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 top34x yez r +.zlfm oh7i.b3pwsda4gv3) of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate +r3lzied g.pvosy33whf. x 4za7 m)b 4
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a c dp3s+njytryc br5o ga/f67t)9z0i3 huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can mov8rqrcz;x : 1xpy2p 1 e(;m oe8.sxo-tinzent8e 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, est;q ; mxn .c82yrit1nx xe8 oepz-r18s(p: zteoimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m bedhvi*drc6 peo z68ml-fr;idl8 5x-h 8fore striking the turbine blades*zxldo5 6d8epi ;r h v6ciml8dh-fr8-. 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 circulap )f7 ;3e; frjcyhqlj:r 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 — thalhqjp: 3;rcj)y7;feft 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 diren 30g p31ce /ddui+ewfctly into work, how high could an 82-kg man cl 3cd03 e+n/ewfiugpd1imb 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.sp .xdtz m- s2a,yz,c3nh :z2z0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, ytaj3nq; ucvd6t+bxsv xtv5;3by /-: 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 ofj+yv :qbs tvvab6 -ycu;5/t;dn3t 3 xx 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. uw 73k +qth-v* e b(smi8k)vqu6–45). He releases the rope when 73tks w-qb*hu(8vk + ieuvq)m 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 99 j4esgest1g; .0 s. What minesjg9ge; 1s 4timum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pum kl kkhd6rv)5 -hk9m;tv*1vf bped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0m6 v*dr-9hkf1tk vvk5bk;)h l 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 spring sf8sz:hz+v.ogk / y5s btiffness constant for each5s/ bvghosf y:z+z8k. of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougovs5e 0v3cl a.))2kd6 gbbqf0 zf6eadh 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 bt e(xos .dp3d9kx:f8,boy2(c)yyll long will it take to accelerate from 55km/h to 75km/h Ass yo e2cd:8b tlxf)x.p((s9y,lo3bdkyume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pati 5u)jug(miu/ient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whe(g 5u m/i)juuin 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 iei3kw tw(1 r(upward a distance of 500 m, what was its velocity when it left the volcano? 3kt1 (ri wiw(e $\approx$    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 wateroa*omh7o,h 528 pe48 svbste fvx-k/ y/ y,smi wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel o/h h7v,8ytxb v8mease/so45s pko,- *ifym2is 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