In what ways is the wordky:u7 / jvs :sirw ybvz (3b)o0/cm;bt “work” as used in everyday language the same as that defined in piz3km 0uwbs/7v(/ y )jo:t:brscbv y ;hysics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Ejqid2 8;qks j7xplain.

Can the normal force on an object ever do wor1 s(er2 x-jjx)bgswr(k? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she(ua7 7uvc zee :sdzi: jacr(e8f ,t;5l0*wduf doing any work? If she l(su7vz, f8 ; a eadr(*0tidue5 :cw7 ef:ujzcstops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always neg(o53cxprr.d gative? [Hint: Consider what happens to the disr p (dg.5co3xrhes when you pull a tablecloth out from under them.]

Why is it tiring to push hacw /ce1* u4q5h7 uaypc jxfd63rd against a solid wall even though you are doing no c qjc 651h3py/7cuad4*e w xfuwork?

You have two springs that are identical except that spring l is stiffer than sph8u;acb5 mq z/ring5um;qcha/8zb 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 +9*o v0i9da3.yefv 0zot3i v5nt iq vwfree to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has d.v yi0na q590v33o+oz* 9 ef twtvviitraveled 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 n*y9ilw k yv0e/8ja 36qs* gjvmuch does your gravitational potential energy change when you jump as higv sq 6a *w l9ek*nvj8/jg30iyyh as you can?

In Fig. 6–31, water balloons are tossed i/0ny7tslz u/5 gz+el from the roof of a building, all with the same speed but with different launch angles. Which one5n e/luz/yltz0i s+g7 has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above itqxhx d- q wvb9:(ke13fqdn4x:s 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 directd43 xw9q:xk: vbdqhx(fe -1qn ed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress t p8 tk79 ymn )w-es7wyym5rcc,he spring by pressing down with your hand r77m-w y ntks5wyp,cm8y)e9c and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from (ecr-2q o:f vdthe ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the b: d(qfr -cvoe2all against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitatio*v09gs5c t pconal potential energy when water at the top of a waterfall falls to thv9 sop gt0cc*5e pool below?

Describe the energy transformations when a child hops around on(efb0ws g +t95wfu )dq-3ujyb a pogo stick.

Describe the energy transmglr i*g4 ;8um:nb 8eml/x ha7formations that take place when a skier starts skiing down a hill, but ah7g 4ui/ gbl;lrexan8m8:* mmfter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hil2 kbn1m;y -n rkc9u1uzt(d3w pl 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 thrwk92unk;nc1 3up (z mt -d1byere is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log inqcg .vppq6y1; their path rather than stepping on top and jumping down on the other side. Expl.qvpgcy 1pq6;ain.

Two identical arrows, one with twice the speed of the other, are fired into a b3z)hmwn 07dea6xq*c7q 7do80 tt(yid xvl)g jale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the sl()6cxj0wdqln q vad zgi7t0eo8 t 3x)77my*hdower arrow? Explain.

Analyze the motion of a simple swinging pend /3jg z66opjro0*3h;asi42lvzkf ygf ulum in terms of energy, (a) ignoring frrjyf;06* zlkf o6a3oz32s4ij vg p/ghiction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it reqf) xkyg52g w-e8 nk1tbound to a height greater than its original height? Explaiqgetk25 gfkw1x8y)- nn.

Suppose you lift a suitcase from the floor0p/ x hkhw*;nw to a table. The work you do on the suitcase depends on which of the followi0 n/x*hk;w whpng: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the woq:-o :qq6y9mndslzl. rk.

Why is it easier to climb a mountain via a zigzp aaa/z2j49 ( bnvx)dnag trail than to climb straight up?v )b9/nx(2apdzaj 4na

Recall from Chapter 4, Example 4–14, that yim i+;liy0b1yxqof n9 w cc/-:u3g9v)fq 9fnfou can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope musl0y g1-+39: qf biuiiq;c v y9xf wfcf9/)monnt be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational fhyhk8p-zm ; w.orce when a 265-kg pile driver falls 2.80 m? m; wyz k.h-8hp   J

  A 65.0-kg firefighter climbs a flitvzv7h bg ; 6cr17wpj5ght of stairs 20.0 m high. How much work is rehjr1bvwt76; vzgcp 57quired?    J

  A 1300-N crate rests on the floor. How mucp)v j5-tg3t6i pgui v4h work is required to move it at constant speed (a) 4.0 m along the floi 5t3tivp -uj6p4)g vgor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 16+v;3w yn8ua sj0-kg crate 10.3 m across a 8ws3;j+y au nvrough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceh,4y( yz*n t ucu,ltg1lerated by a force across a floor at a rate of for 7.0 s. Find tug1lu *tzyhn4( y ,c,the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How much bodhe dji8 by/dqd;e7.zzc2+ 2 u k63swork is required to stack them on;jdu d3bhcz+ 6dqk z/ 2eedy2.b87osi e on top of another?    J

A lever such as that shown ijxji 1vk/i6m(n Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of ikijjx6v(m/1 output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 285mv 2pb2zhyx eo;*zu2° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coex v2*bo5 yp;uzh2m2zefficient 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 gi 2 rm pnzs,nw5*sst,h14o- hhove a helicopter of mass M an acceleration of 0.10 g upward.1h5sowh,pn, t s o -n*z2hrms4    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 t:sp dikf( 4mi)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 axis, variessk -zhfmdcc7 g1w304h as shown in Fig. 6–37. Determine the work done-s3hh 0c dcwgz7f14km by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particnrdd/l txnphqjk)g s-)- (hf52r +1ljle 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 mawp;6c jm6rg 8dss 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 increa2cbw4a6d*2g31wc en z/ nnihnsed? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is reqe hqf-(; veb0r( 2rtg (qvbk5luired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 2 fk4we:yw*fx7gt r/z105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fr-tx)et-ly)vcnba - 78 q. xtvmom a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of )tnx)-cq -v blt8 .vyaet7mx-the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove4dcrd v 5mvqm9*v+qz1 backward 25 cm when the bal1 dcz+5v mqrdvvq m*49l is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by whatchd* -sa k h8 8r(nvfotp;,lb6 factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s re;v*h a(lfcos-kptdbhr 6 n8,8action time.

  At an accident scene on a levi4yy/ic- gz4hb a xl39el road, investigators 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 estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) th-4x3/9 hicbaziy4lg y e 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 thfjl/q/( e;yig e plate, it may have yl/j ifq(e g/;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 thrown straight ux3bpav vdf 5:0r 4zne4p by someone who does 80.0 J of work on it? Neglect air resistanzvrb d:40 3npvae4 5xfce.    m

  A 285-kg load is lifted 22.0 m vertically with an acc xzn6x+lvz a)-vtd)l2 qum /-leleration by a single cable. Determineqnlzxlzt+u6m)lv x )a2v-d /-
(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 muskt6owy0hrok6 0v 83e vla. xk8m2x l8lbkar.9 t this springxmr6o0v a.r2 yo80.lltklh 89 e6w8b kk3kvax be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branx r;l l,m03d4hbj1gmrch to another 1.2 m higher. What is the changel rj,ghrd0l4;m3bm 1x in potential energy?    J

  By how much does the gravwho v1omn 1w-qv:w 1)yitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during thh w:1wy wvm v1q)1o-noe jump?    J

  A 1200-kg car rolling on psj qk c6tov u0lfb0o8;k(is3 vg/(*wa horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in cfkq80(ibvs3uw (*vots kglo ;6j/0p 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.8rtu x rn1p c9c*)/v*g o eajedp.oq6 from the ground so it is 2.20 m above the grouno*t )ug8/q*on a.9ecvcjpr1 pxd re6. d. 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 elevatioge(g +j*:w jk, tb5xfon of 1600 m and climbs to the top of a 3300-m peak. gx+b5*j( w f ,etg:koj
(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.j6,qf-+2 4nlilhu 9n e 6xdwa c6nm*nk The end of the spring is next to the 15-c l6-nx66dq+iwj , eu nafcnhl*4mnk29m mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a jg8wre t 2x9;sy72ysjuik 42zvine hanging vertically from a tall tree igz2 s2uykjy; 29i tj4se8xr7wn the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35.0bpq hbyo5.)q) $^{\circ}$ 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 showm kf c-g;bbled g. -kg+(im++8u fbr4ve up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetfix4 9+izb7l2+2*q r z)hfb(bxai b usic energy is transformed 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 m and cross the b9bz2* zbifqr(i4 h i)xfb+7xlb2us+ aar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of0m. 70r8t c lk2gif aftt3gy (i0shlu- a platform with a speed of 5.g(70tli .f cfym0ls ahi 2u8kgt-0t 3r0 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 (ignorehcn,s:q0 t8 ps its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) W,:0nph8scst q hat 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 shc)i3yft,(ij4cea6 e0 ;dh): dp zr qfiown in Fig. 6–39. If the block is to remain on the track, even at the top of the cirrdfay4q)z c0ec ,;6 3id )ehp( t:ijficle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end9oks.:l k9ud)dis. du of a spring (spring stiffness constant k), Fig. 6–40. The block is uls9k :.od9 k s)ddi.ugiven 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 bungee cgop.2 yd;qk8tord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assumikt yqdog2;8p.ng 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 t0wpdq:kn1 my )u8ykzhd 5: u9mo point 1 where it is released from rest. Assuming no friction, calculate the speed 9muz yw ukd15hdykq 0m8:: p)nat points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s alhazpj- 8g 7z4t 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 placed at the bottom of a.yy8rk.2prkvyl ; fys*u:cq 0n 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 constvf:r2pc;yr.syk0 8u.l k *yqyant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle r gbz5lb0;dcwkh i((+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 q +wxqtq1a6+ d8ak, cxopposite directions, collide head-on and come to rest. How much thermal energy is produc6 qq t+x8 ckd1qw,xa+aed in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottomvbh7q:7nm iq2qmut0- -ubzha h m;6 n. with a speed of 2.2m/s How much thermal energy due to friction was generated in th;qihb72qmh n:u6m a.qb0 h -7- zuntmvis process?    J

  A ski starts from rest and slides down a 51ooe*or7o ph(7dvnu5lx vb 422 $^{\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 13j198qggg *jj v.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 bounces back to a height 4l el6p6kf1g1y cf5bqof 1.5 m. q51l6ey4lb1 6 gpc ffk
(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, i8x. xfmu o2x )9ou2vbws pulled across a floor with a constant horizontal force of 350 N. Foooux8x9fwu m )2 v.2bxr the first 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 passesqqphz4wy 2+eps8v2kv+y ( z :c point 1 with a speed of If the average force of zyh8ep2sq +2:(ypzq+ wc4vkv friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a q-gu ppcgd(0st:00zu, se .ufsteady 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 horizontal ecp d. zs r1vb;b /-ud/r9ibb7spring (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 frvr1sp.u db7 z/dci9/e rb;b-biction between the block and the table?   

  A 280-g wood block is firmly attached to a very light wfnj we)/l; jh n;tj)3horizontal spring, Fig. 6–40. The block can slide along a table where the coejj wwn)3/;ef; n)ltjh fficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glidw+zvk 3x+hl*oer” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventualll+ +vzow hk*x3y 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 ton2y 9 ry,up7pn a sixth-story window 16.0 m abovuny, y9p7p2nr e?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be th n nx*:fyav))me average force exerted on the*nyv))n:fam x car due to friction and air resistance?    N

  A 1400-kg sports car acceleramjhji* 1a k1.;,ofvvy8r/oshtes from rest to 95km/h in 7.4 s. What is the averag hvs.,1mio8 vf*jyk oh j/;ar1e power delivered by the engine?$\approx$    hp

  (a) Show that one British horsep7 eo1voa) cb 4o).lcpjo(4bkv ower$ \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 thjhgv8lwq * 3*ke 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 j ci*ob2r:6jnub qe6dc/ib /v4 ye4 2q6.0 s on :6 ebicvq c/j2r dyo64eib *qjb2/nu4the level 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 moto t1od3ufx2r ,dr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7l7 )yv+bhjavmh(pq 3*eu6 w/c .3-kg shot from rest to 14m/s If this motion takes 1.5 s, +jumv7whpc y/bl63(h e aqv *)what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3ajk-a ,+*)/lr pxv 1pjy1yi ki.60 m. What output rating (watts) shouldyrpk k1j-), alipvxy j*1ia+/ the pump motor have?    W

  During a workout, the football pla o kellg xxh3nk63y3 ,tq:4e2yyers at State U. ran up the stadium stairs in 66 s. The stax 3l eq3:436 2ngty,oekhykxlirs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 uf qmo )e0n95u$^{\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./u rnej2d5f. ad7l1vs j n9 -slx.sdc, How steep a hill can it climb at a constant speed of 75km/h if the frictional dn9.2 s5f 7 lc d.sau-rx/ sjd,levj1nforces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to 6*eyod-azg j bg+5:fp r)4.nipgeto1 drag a 310-kg box along a level floor at a speed of 1.2m/s if the co:b6 e*ze4a5gtpon d-)jg.ofyg+ ri p 1efficient of friction is 0.45?    hp

  A bicyclist coasts down al9qse 6: bnr71jd- nfh 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 caera 26pwa yye1*e7g.ors 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 permanently7 ya6e.yeeo g* ar2w1p 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 t5jr0(.h0mgzw qj m;dnhe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all tqh0.zn g0;5r(j dm jmwhe shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (j z*1 yc4ux:ydFig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at la d*yzyu1: xcj4unch 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 looped th54xqw7ro e f-clylx2xxc/5. zi3 gtk(i i7:prack shown in Fig. 6–39 is to remain on the track at all times, even at the verql wx zekcg i5c 2xi-p:ix hlo34/7 7yr(.x5fty top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft withoui-x 29u8 0( i c;k-vywb+s(dbarzema f 1)pcebt his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his teb;e-2p8e( f)+a i xcb 9wm0v1rcyk bd -(uazisrminal 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 cor5 d7k3 tw3d-.zevuy+l( 5jdc msp(ndrd of length L whose other end is fixed (Fig.lv5d((wk73 +d.ytdu ep35jrmczs-nd 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 top of a 3700-m-high mountain. The 6vh- . izrtdk*climb is made in 5.0 h startiniv tzd 6.h-*krg at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevat:) dn,;*rz0bnfj+ia ktso.iior 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 47,000 peop6ozlxptg 51(yk2 g(kz;m:foi le per hour. If the average lift caroi g;kz yg(:( 21fkzpxolt5m6 ries 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 650kg/s and falls vertically 81 m before sj/dw +kr:tdnbywq(/c l;m53 r triking the turbine blades. Caq:/5rnw/bd ;jlk3yd +(w r tmclculate
(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 coast-sd-j.oce a xk0, 6baper with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bd ep6ka .,xc-j0-sbaoottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into worku7 dtm 5s ;3pm)r(fhqz, how high could an 82-kg man climb a3 uzhq(5;m7 smdt rpf) 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 v u *.bxqfl4 d ve.a)ehd-w4e,ivyc-, an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathrooxd:( uoz8p o- /v8u xuzhb5hr/m scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, whhp:dr5hx- 8x(zuo/ozu8 b v/uat 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. 6–c4s0s6uhm+0 *+ g,mnfuij z3m pyf 8ej45). He relec mn+y0u 8gfe6s*pjfz,hs30mji4u +mases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s.82po3po xeu9n What pu9p o8 2exo3nminimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store)dec5x58 3 cqmual/ni energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energyuieq3cnx585d cm a)/l 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 stif 4u;ew0c fapn8fness constant k is cut in half. What is the spring stiffness conspe;un a04cfw8tant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a ri7km)8 m.9v: .oljxzf7dgqqb ough 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 nipu 4b1tw,ffj t;yba+s /)f8in 3.2 s, how long will it take to wun;f,t+i asjtf)/b ybf184p accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the 6 w0k4oem hlu(patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is slopin(ukw4m l6 0eohg 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 dist8;5o jffxc .s+c1tq - qt;rshqance of 500 m, what was its velocity when it left the vot-xcq5 otj;shrqqfcf. 8+s; 1lcano? $\approx$    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 a rate of 95kg/s (a)i 0bgq w-y.2 -hqvnv-o If this water-ow2-i.ybv0gvqhn q- 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