In what ways is the word “work.d amb8 gw/qcjg;nk/- ” as used in everyday language the same as that de w./gkcnm;g/8-qajdbfined in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Exp0fg6 0qxxu e2jlain.

Can the normal force on an object ever do work? Ex 9qffwjm;;g/gplain.

A woman swimming upstream is not movin2h. g4mfq 5clmq f/qc301db uo7du-v ;aavo*r g with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done .ala73*5/0o2v uuh vc1dmg m- qq cfq;4 fbodron her?

Is the work done by kinetic friction forces always negative? [nvnc8 il17fa4Hint: Consider what happens to the dishes when you pull a tai 8acn14 lnvf7blecloth out from under them.]

Why is it tiring to push hard against a solid wall9* bfdiw gk.pady 4)va44j/db even though you are doing no wojd/f 9di4d) k4bypgw4.av *ab rk?

You have two springs that are identical exxh .(s 9.zknujcept that spring l is stiffer than spri.x.(sn uh9zkjng 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 consdvn3,bxyv 9-) khe psd5jyw:6 tant horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest axhbs,v ykd edy-6 j9wp)3vn5:t 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 gravpy4wf i+op s)4k/ku,vitational potential energy change when you jump as high as you ca4o s,k+u yiwp pvf4)/kn?

In Fig. 6–31, water balloons are t2 ,r1h3oo ,ot xnnojd8xc:s 1e1kq8owossed from the roof of a building, all with the same speed but with different launch a ed3ohn1nsrwqx o,ooo t,xj2c11 8: 8kngles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point ing hn9l/w 65t+zzc pwu0 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 fromn wt+lw 50h9/ pgzuz6c the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress t2zv- b c9m*6i qfxi*pit gs)5bhe spring by pressing down with your hand and then relz-ii5i*vb*gb cms6ptq)2x 9f ease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung.,cde.tfa; ptew .o )g from the ceiling 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 injc.t.op;gwaf) d. te,e ury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential enerqfcvj* e 36w e8c*gah8gy when water at the top of a waterfall falls to th8 cc*3q6e *hewvga8jf e pool below?

Describe the energy transformations when a child hops around o9xs6.c :vvor)1dcgybj p8w*w n a pogo stick.

Describe the energy transformations that take place whe7i ksa.la/ tsmxw* x4(n a skier starts skiing down a hill, but after a time is brougiss/ w mx.7kl a4(*taxht to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heighx *q5id mt(hwb/h9qc+j7ezr 5t h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy a d*qbwjth/5chz m95 x+7( ieqrnd there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in -lh 8 y01ds0pe+sjc udtheir path rather than stepping on top and jumping down on the othc80hsde +- l j1up0dyser side. Explain.

Two identical arrows, one with twice the speed of the other, are:rt ljta-+p l- fired into a bale of hay. Assuming the hay exerts a constant frictionl:l r+-tptaj- al force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulu2rm,aqf k5z6zus -e np*c 0ue8m in terms of energy, (a) ignoring frictu p*m0s 68zu,zeek cn 5aq-2rfion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, ydete+(q 4 9)(vu40uis +fg:nsjxbtycan it rebound to a height greater than its original hevyq gn u)dy s4efbt9 e(04x+jtui:+s(ight? Explain.

Suppose you lift a suitcase from the floor to a table. 8:d3 oo, l5njjjq1hflThe 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) the time it takes, (c) the height of the table, and (jo fll:, d5h o3qj81njd) the weight of the suitcase?

Repeat Question 22 f y9 esohy9)4miq884c:x rgqob6t 5zisor the power needed rather than the work.

Why is it easier to climb a .q;wqdel 0fr1mountain via a zigzag trail than to climb straight upr0q 1dq; f.lew?

Recall from Chapter 4, Exaju5y;e4xix9lra) lr4 mple 4–14, that you can use a pulley and ropes to decrease the force nu5l)riej 9ax4 l 4rx;yeeded to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fwh:u9- zldyobo m88 i2alls 2.80 m?:yumz82 ilb9-d8w ooh    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is c,ge : l,su0/repa (tsrequpuesagsl0,/( erc :t, ired?    J

  A 1300-N crate rests on the floor.tg ciaq(01(.y5ii3t h8bvzhpn2hb i 2 How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forcegp5htnzih0ia b vbq2(.3 yi28h ti(1c of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) py)z 2gi)anblw; q+xi :ushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.5: a)byq2n;+g l izwx)i0?    J

  A box of mass 5.0 kg is accelerated by a force ai(eebp s:0uuobj m j2r5li/c+knk1)-g ( jkv(cross a floor at a rate of for 7.0 s. Fin (l/b um0g2o kn5spe)+cb1ivji( ure( j-kkj:d the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table2/sk9bn)w jb6d(cxt f . How much work is required to stack them one okt)9s2n6wb/bxc jdf( n top of another?    J

A lever such as that shown in Fig. 6-35 canx fk)6,jnd,t k be used to liff objects we might not otherwise be able to liff. Show that the ratio of o 6, xt,fnk)jdkutput 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° izhr0 -+dpyx*qmjn ; dc s3y5k3ncline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36).0j3hr pzc qmnd * 35-;sy+xkyd 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 accelj0yzm7g ,ww9 teration of 0.10 g up 7jgw9 wzy0tm,ward.    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 tacd e1c+upge 6b, c9gm.+vpd-qx ps3 ,he distance 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, acting along the x ax4l)hgyem8 s w5is, varies as shown in Fig. 6–37. Determine the work done by this ms45lw)heg 8y force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in the ;o-w s,ilt*gb $+x$ 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, a-.8jdl o5l(ft zhntr2n 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 d8 /14ptswitxifyr)5 houbled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop ac ebzk(; se+nd8nov(/ n 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-kg;z8 :iwogzw3icar 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 ofm-6io1: tn1 kqw b0nbz 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bnk 0boz6m bit 1:1wnq-ow?    m/s

  A baseball (m=140kg) traveling 32m0c9w, r) nb/5ykiz/x*wt pk lrsu2k7w /s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball opis/yul z*k,wb2n tkxk5r9/wr07wc)n the glove?    N

If the speed of a car is increased by 504rgu 7 n e6 qz-t12+by; viyszme-n)fh%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore th-sn y1n;t bzi2 f)q4+z6e7 -vre hymuge driver’s reaction time.

  At an accident scene on a level road, investigators measurc*s;cpnd z(:t/r))jv ia 1ugme a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brsmi 1ur c/* tj)gz()n;ad pcv:akes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the timeqd2d2.//ddsea dkvqs e +wd 4xi)4 /dc it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force /ed 2/c2 qd4dsd/s.addwveid4k +x) qof 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 thrwimf:i)gn;f , own straight up by someone who does 80.0 J of work on it? Neglect air resgwnfi:m; if), istance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cabe *amlcx (cgk,p5z,qhp o:r55lkq, h( 5o,xp5ag zmrcce pl*:5e. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much mus :9)steqha 5b soa c5mx0r(3pct this spring be st0pa3ax5rqsm hs(: 5eo)bct9 cretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch txevy)-qw-y j8kfq4q ; o another 1.2 m higher. What is the change in potential energy? v-x q4)we-8fqqy;kjy    J

  By how much does the gravit+hu7qkf/nkxfs r ux+( + ydv47ational potential energy of a 64-kg pole vaulter change if his center of m(/u4 qsdvuxkn++x 7fyf r k7+hass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v d 7fu xyzr)8* rruk.97 uu4 ibm6zudd2= 65 km/h when it strikes a horizontal coiled spring and is brought to *9fkzu7x zy7) ru6 ud di4 mr.r2du8burest 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 grokr o1 48nraeo3io cyz88l;w/k/p 7osmund so it is 2.20 m above the ground. What is the pooon/i8cpywrsa r7klzo/84ko83e ;m 1tential 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 tovu;ui 85o 8n luis6qs5p of a 3300-m peak.oq858 ni5;uvi su6 lsu
(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+ anh 41ml; -zqdpzzmwyd,.)o ruler. The end of the spring is next to the 15-cm mark on the ruler. Ifpzdyl-mmzza +n,o.14h ); wd q 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 (5.3m/s) and grabs a vine ha/j 34stn(ozyb .gu,t7, le3p s ,rfx 5eyk8uppngs sp u7(jf kr3y/u,ttn,eyzgb3p.8,p o5l e4xing vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slid-vzd:/*me+ ayhjdz 0ves 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 *j+f vsooldgd q -f;6+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 gravitabw3arc)lx ee2i, h9n5:b aty. cxd9 .ftional potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift c .hy c ln9tr eew:)fi5da2xb,ba .x39her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from tws k.* n*dpf5ts horj8s4e 28khe top of a platform with a speed *pns oe2s*.j885sd4 wkfhtkrof 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), afji(vcz66;pb xw/ lz1b /k.a whose spring 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-k(6xf/wal 1cza .6pvj;/ bzbki g 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 frictvp pnn -q5oeh;tt7 34cion along the looped track shown in Fig. 6–39. If the block is to remain on th3qo5pv 4hte7 pt n-n;ce track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffne-ze kdt9;w29vn1rju8ce(r7 k3ffx /n+ uehi b ss constant k), Fig. 6–40. Thf8xvr+9-/e23u nez 79ik jutwn1b;drh (eckfe 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 bu; 8b;*zunoeyw 81qclo ngee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant neyb1u8 qcl ;wz; 8oo*k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 wherif 5vw 1qkn/.je it is released from rest. Assuming no friction.kn1viqw5f j /, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sn 8w iif8v,z)opeed 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 placed5 +.ubtivd5sd:b ttl5 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, calcula +5 :tdbs5ub5td tiv.lte 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 c dl/ c e6ntwir1bsa79)ycle 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 kw yo cs x0i:2yby/a.o) w19eadg and traveling 95km/h in opposite directions, collide he19yywse:x.i w2o b)a y0ac/d oad-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bott5)h9. izkuie 0 oyemlw507zlzom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proyo0 mu ezi9.kzzil w05e5hl)7cess?    J

  A ski starts from rest and slides dow,*3k( 9 shocq+xs jpiwn 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 h/j f9twf+ma9s*e rb*qrk :6t 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 s5 5;w:mzs42iocru.fw2i brv m, and it bounces back to a height of 1.5 m. owrz4. 2uiwri5vmc sfb:5s; 2
(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 res9ywcg9sihw b-g awj.o:3fp:, t, is pulled across a 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 f9 :h,g :iwb9joa- wgwp3s.yfcriction 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 :( k/qtrxkb6s)w- :m0 a+be zvqv9lmx a speed of If the average force of friction is equal to one-fm+0x: s:9k) mvq vk rexzqlt6b/wab(-ifth 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 a steady upward 18.0 ses +ac(edqts :v ,46n 8o+rzl$^{\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 vyaj/ *2o49ooq(u -(cw/b 3 ttjbnikleery light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the t-cbt a2*b3l/ok4j(u oqt j e(9 inoy/wable?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6–9mccx*8.zj1.ncsm7hkif x yo gv 2 d:/40. The block can slide along a table where the coefficienc/n 7vj92cohi km sfcxmgx1.y 8*:zd.t 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 spenb+o ta av+ 2nu:y4f,ace shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence oey bn:nu,t4 f2 +va+oaf 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-kj.w /eqf.xm -qg piano to a sixth-story window 16.0 m a q j..w/qx-mefbove?    s

  If a car generates 18 hp when traveling at a stu;0,ph cae+tfeady 88km/h what must be the average force exerted on the car due to friction and air resistaupfe;hac,t0 + nce?    N

  A 1400-kg sports car accelerates from rest to bf3byjzthg9 ) 7/w+ept)) hzg 95km/h in 7.4 s. What is the average power d+ g)tj fb) gh)tz37phbzw/e9y elivered by the engine?$\approx$    hp

  (a) Show that one Brie28t,j c;nvhj50wwxi tish horsepower$ \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 pyz8jb ugqfa-m0ay/h 7:eh 37in 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 downiq)gubnu; pjl*3bet 9p4h6:u from to 65km/h in about 6.0 s on the level when it is in neulp u);j :6q9*nh e4gbp ui3tbutral. 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 ju+ ayh1-ejt9 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 I;g vi8i9xqgn 9 k:8korz/i/-sqen s, if this motion takes 1.5 s, what average power was devel,/grn9e-nxq:;i s8z oik /k gq8v9 isioped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a.+ek xx* t*/spzryu;c height of 3.60 m. What output rating (watts) should the pump motor hptescky;ux z x*+r/*. ave?    W

  During a workout, the football players at State U. ran up the st wgq;dj9bn6u y-zye13 adium stairs in 66 s. The stairs are 140 m long and inclined at an ang;e96qgj3 yb n1yu-zdwle 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 cl;;iag,pwjkk/,n8 r bdimb 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 output of 120 hp. Howi2it+c9j g8/wtb n6of steep a hill can it climb at a constant speed of n t 9+o2w/8fjtgc bii675km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have *tuu0ufqa- mi-rb,0zto be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if ,f --zqumur 0 ut0ib*athe coefficient of friction is 0.45?    hp

  A bicyclist coasts down fdmkprz0k7lqde ,1- dl2d6 b* 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 cars have built “5mi/h(8km/h) buj(md y icmpn5(r+ .9omke:/pampers” that are designed to compress and rebound elastically without any physical damage at spee.5c(n+ m/e oap(kdj :rpm iy9mds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the fir mflu:bp gmb:4/rr;zyx 6 (e u(xu5/ayst shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assumip:br;umu:/5yx( ebx46mg la r/z(fuyng the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42)zu4do, ,v 3:*adu ljcw in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he wasu l4 3*z:uvcdw,oj,ad traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withouti gflsq0ea*c, sp/3v 8 friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very p lqg,3a08*csse iv/ ftop of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his parach8uam ,,vey7ldute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only mie,a,8dl7v y umnor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed pt1ru l*e;s/s+isl( pofm0/sd,zjg4b y 4 2pz(Fig. 6–43). gtplo2u1 4,z;40pfsr dpms lsz/s/+i yb(e j*
(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 3700-5rmwrgz90 u8km-high mountain. The climb is made in 5.0 h starting 09 kru8wr 5zgmat 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 whep lk:k0;yg.07 7t gy1qtbuamb3a dr 2gn a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move e8 dw/6ywq*oklk,r h8 w1gpz3x0ngl* 47,000 people per hour. If the average lift carries people abo wqpryg/8d x8okl3**hkg1lne60wz , wut 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticae3dl*zf d/+ yn efp4.glly 81 m before striking the tz.* pd /n4eyef 3lgd+furbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (F+6p nbirsss.- )d 4susig. 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 min i)bss4-.nd 6sru+ sspimum 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 jj88vmeb x3g;ow+d la u l,(+m-eou:p directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar ma,pxwlo u3e j ;dlb+e(v-ju8: m+o8g(=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 upwa4+x 2mk)1oyndg hss4ba sx9l (rd 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 bathroom scale, the spring qc9 /rm hh*wf+inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if yo fmq9/ hrw+h*cu 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 ex1qak.tm8eggv; t +,at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when hie;.ktaq1 +,m e gxvtg8s 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 2w,p(fxy cllg)2ti y072-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to acl l( )fc0wi ,2gxy2tpycomplish this feat?    W

  Some electric-power companies use water to store enec)efm(nj1//u o1;vsf7bxy uxrgy. Water is pumped by reversible turbine pumps from a lo/sj7 (1funmc xbf/;eyuovx1) w 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 half. What is th595hwnr s gb4tgr(bze94z5f7qfne-p e spring stiffness constant for each of the two 57bgg-s95bwzhnq 5reref4np9t zf (4resulting springs?   k

  A 6.0-kg block is pushed 8.0 m 2jkpkx(i9h 7di :n.zcm nze32up 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 accelern(rf- txz3 wekh st-xk* )4u5.nctilet d)r(4ate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fricx(53 et thftknr4-xwn.r ksetd i)c*-l4u) ( ztional losses.    s

  In a common test for cardiac function (the “s0i)b 6ya0wz a//kj vpatress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate)w /00a/aiab6kvpzj y 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 ver*24g q emzmt/,aohu-v tically upward a distance of 500 m, what was its velociteua/mqv4 z ,gto*m2h- y 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 heighp6so b7sfzv-5wf*/o it of 2.0 m at a rate of 95kg/s (a) If this watewo v7 5sifo6fb/s* -zpr wheel 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