In what ways is the word “work” as used in everyday language rb- fpn o6yx0 +pg:v 21)asmj2yin-pd the same as that defined in physics? In what ways is it doj:s+ dv- f-ryypx2gin)0p2b 1a 6pnmifferent? Give examples of both.

Can a centripetal forc2*z,5-gvjtknl:6gm vbtue n:7)ymoky ;swb+e ever do work on an object? Explain.

Can the normal force on an object rhzoqimnhs8 g+ m 3 nu0k-2:f8f+m/cjzmc x18 ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she d4 qmyr5pe: qi+ )mgww)oing any work? If shmq)ye m pg q+4ri):5wwe stops swimming and merely floats, is work done on her?

Is the work done by ke5m +unf-ox5k,q/od u inetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecx5uef5nd m+/-ok ,uqo loth out from under them.]

Why is it tiring to push hard against a solid wall even though youq8qw2.+qzv6 cy,t hve are doing no work?v.qz,qc6yq82v teh+ w

You have two springs that are identical except that ps ,gs0 ;kfhdb rg3an4mx957rspring l is stiffer than spring 2 n390xfkbar5 ;ps rg4h7 msg ,d$(k_1>k_2).$ 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 horizont;ctrd rce-6i3dpnz s):pu 8v+al force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled p- tuc8c)ddn6ri+:s r3epv; za distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change when i+3uxyo djt,d lhc)4yu9 -d* fyou jump as high as y *o 3+9chdu4xdyi, -lyfujd) tou can?

In Fig. 6–31, water balloons are toss h lh shu.n ;7dq6eu+:hq zu3ii67(ezfed from the roof of a building, all with the same speed but with different launul uuq;h.:dz q6z f377eie(+s6hhi hnch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above 5bctz bys;e0) 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 alo)b 5bzystc;e0ng the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests uprig+7rbd9o n,t:u eayjy )ht on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the tabluyy tnd+ rj)7ba :9o,ee? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instrucl-e-u-lm1wxb2 *rywet+,bvs1vb z8ptor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is suppo by81xm2z,pw s-uebv+ v* --rl bw1ltesed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of w-h-,dvf(wclxbj odz-g dy64m k/ 25c a waterfall falls to the pool belowmvb -d/j(c -d-6gcxh fkw4z y o,w52dl?

Describe the energy transformations when a child hops around on a pogo b2x- m55ud7n.lr aa6(g;,mrly bubws stick.

Describe the energy transformations that take place when a skier k:la l(,ro*xpn:0 lai, fw:vxstarts skiing down a o(:x l:,aw0f klx,p rv*li:nahill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at thup1c 7 f1cm0-obpwxrbij:, l6e top of a hill of height h and sliducppfw16-c x1 mr7i: ,ob0 lbjes down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step th1*j;ci6*lw na 6na dover a fallen log in their path rather than stepping on top and jumping down on the other side. Explain6;*adjtan n1 *6hiwlc.

Two identical arrows, one with twice the speed of the other, are0uz mgd*dw+mnth akn,h ,ko4m+-d u,/ fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, t 4nknt/khmoau,+z-dd mu+d , w ,hm*g0he faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pen0j4i c)ira: hydulum in terms of energy, (a) ignoring frictionar jy)0 ci4:ih, 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 hh wlaq61*/+mbnn2by leight greater than its original height? Explai 2myw+lh*ba/1nbnl 6qn.

Suppose you lift a suitcase from the floor to a table. The work y d6*arz0st6uliy /l40w d5it kou do on the suitcase depends on which of the following: (a) whether you lift it straia u6kriy65t td i40zld/w*0ls ght 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 thagt xoa*s:kw7w3r s,fy v(:6yf n the work.

Why is it easier to c :vu u8njz u/mnqs2h5vn8sf9*limb a mountain via a zigzag trail than to climb straight up*fj zus5qh/nv mn n88:s9uv u2?

Recall from Chapter 4, Example 4+2d c4, ulqui)w7uldl–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But fo7i wd)l c4u2,dl uqlu+r 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 wheni*krn9-;fl+ge)z x4 i pwrd*l a 265-kg pile driver falls 2.80 4e9i n rg l**lkfzd;x wi)r-+pm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hip ief e9py;,0r0ati-4p4fr zpgh. How much work is reqr4900r,yfe4ieppa ti p pz-f;uired?    J

  A 1300-N crate rests on gx*.4b3rckn8ac + nnwthe floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forcek + na4bg *xn.8rcn3cw of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the fm2z. )7nwv/ iu+mgenmovers do (horizontally) pushing a 160-kg crate 10.3 m acrossw+ev)n .mn/zumifg7 2 a rough 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 acn;i; )yly 9 smc2uops1ross a floor at a rate of for 7.0 s. Find the y;2p;cumn 1 yio9) lssnet work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on ae -z*h5u5ztqyee,sj d2 t3xi- table. How much work is required to 3t5je-5qhe zd2xyut zis* ,e-stack them one on top of another?    J

A lever such as that shown in Fijc1q0)ddvr8g p od(; ag. 6-35 can be used to liff objects we might not otherwise be able to g0p od;adjr qc) 18(dvliff. 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 down a 28° incline.u98p75mxqkv xx o/yv and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calc8xy pvv7xko5umxq.9 / ulate:
(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 yme8syz(, +j uhelicopter of mass M an acceleration of 0.10 g upw, z(eum+yjsy8ard.    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 2fk9k .gmek*g 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, acting44mp+oe bx52zy 8ze6h 3y mo*r6wmt bi along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move xm8rom3*o6 y+5e42bbw64tz hm yie pzthe 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 actosiu /rxav wjto++ uc1ls) p9t(-1r;ns 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 mass + 5idj p8aow5;v sit *dow97aoof $5.31\times10^{-26}$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 hemm zoy/.x5b//mr i a256rsob as 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 stop8go h+*bb mp99k0j xlp 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 1(kuo+w.-q 3 lfuq,q w7tczv i(250-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 1lczvzv/0)h -,:p trfj10 N on the a-,v/0vf p)t j:zclzhrrrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves 8 vl; ecn3v,tla fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the lenl vc;,tv83ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum 93,gf8xafj mr braking distanaf,r9 jm3fgx 8ce be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure od pw7 oa0:.xxg5j jk*a car’s skid mark to be 88 m long. The accident occurregx7 j 0opo:j*wxa5kd.d 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 brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched*t qk m-k8j1of at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the avek-omjk8t* q 1frage 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 th;i r2t8kv fo- m2ovhy2rown straight up by someone who does 80.0 J of woiof 2tv-v8k;y hm22rork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m w.258 u h4m wkvg88v0x07 xu)xozkkkf ppd3xj vertically with an acceleration by a single cable. Determwv87pd.x2 3 kxkhxfmpu k8oj )k0u0g4x5 wzv8ine
(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 muc 0,xweopdx;(i6 m1wqlh must this spring be stretched to store 25 J of potential energy? o1 ;0mwxldweqixp,6(    m

  A 7.0-kg monkey swings from one branch to another 1..zf8 p(vb + a0dtfj)5j9lrqj c2 m higher. What is the change in potential energyaptjd(f9qf+.8r l bvj 5)jz0c?    J

  By how much does the gravitu jpo0;g jk88e7lma,lational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m durin8lpo,ljj e;87 0mua gkg the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6:3c u h7 b)say4,hvupol kh(g35 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the springsh )7b,u3:cukoyg 3hphl v4a( stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m abon a zut+dn5 ldy6i)g6-ve the ground. What is the potential energy ofyduid+6 - )5al6tngnz 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 top of ux 1ja tt-en3qc3 dg0(a 3300-m 3j t0-e1ncxt3dqaug ( peak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the spg bz:v1hf50+ jv6pdri ring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will thep hg56divf+jr0z:v 1b 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 i5p1gklj ;du ;/tsbx 6 vx6dom.3-ptnvine hanging vertic p;di3.v5xl tdok6x mn; gt1up/j6s-bally 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, slides dco6evrli (x k-33wb2d own 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 shoi65d2h19eg rs q 0o taq,fo/j1q sdu5hve up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into grav kr;j4jx2-1fa br bk*(0( d6jubaiuccitational potential energy without the aid of a pole. With what minimum speed must Fran leave the grou brxbuur4fc( 6jkjj*d ;i1 kaa -c2b(0nd in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from thei3zk;mr lz:uxl 2e7.t -w(v li1x :taw top of a platform with a speed or7 lk:tw:. w l(zlvatu 2zieix-;x1m3f 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 95514 an2 rrnhlk0N/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 r2an4r1kh5n lwhen 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 loope;7 di1vo bw4wqd track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h bo4 ;viq17wd wmust it be released?    r

A block of mass m is attached to the end of a spring (spring stiff z,ve-fy1ld)f ness constant k), Fig. 6–40. The block is given an initial displvl1 fefy- )d,zacement $x_0$ 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 frw4d( w z6kl+u ih3)psa97(agw dfmzwy.pn3 1 tom a bridge. She is tied to a bungee cord whose unstretched lefw(3)tza l w1swyd.pgk6 9wa+pn4 u7 zim d3(hngth is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to pointy)ll q rc;9vymv;hn b3q.l/4e 1 where it is released from rest. Assuming no friction, calculate the speed a;mr y 9y3lvhceln)ql q4v; /.bt points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angl30vcr,q6 yu o+jq*j pue 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 aemyl +uzp:3a3unz7 fzk+* k3k spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration ofk*k:zkyz3e3n+ uflm3 a+ up 7z no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up ae8l1zircw*nd: 4ut83l g l0v l 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 oov :spmf4y+ qj6ymsw 9;mva);pposite directions, collide head-on and come to rest. How much therm4pfj9 6yqswm;v)a:ym; ov ms+al energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slib odb3b ;inm7p(use58de 3.5 m high and reaches the bottom with a speed of 2.2m/s How mu o(d;mb5eu87 nsip3b bch thermal energy due to friction was generated in this process?    J

  A ski starts from rest and sl* * eo)5n6:8oauuqn8 u5u)ta fpelfcxides 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 dropped from a tree 13.0 m above the grounf4 j da43erbzg f8x:h3d.
(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 hipo0 ksn7o:d4eight of 2.0 m, and it bounces back to a height of 1.5 m. dk:nio 407pos
(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 acro z1 mcqpqxu8c(9uwhr -21fs*fss a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for t8wc z*-mfc2hq( qfp us9r x11uhe next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If the 9 t5)gk*xi*2cm f n khu6cv2ojaverage force of friction is equal to one-fifth of 9) 6*c*xm2ci h jt2k ogfu5kvnits 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 t .ukgc3r gz6q3f/x1eob t93w b5a 9vazhe 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 horizontal sp28pyt0*ub5gvfot4 n o ring (k=180N/m) as shown in Fig. 6–40. It is noted that t8t5t0y p *vfgn2buoo4he block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very ligh9 5o iss7gl(fyt horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the sprinfs7l 9g(5ysoi g 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 cd1qakb7e;7vs )y d-n,wjqfe sdo la.8 )k 5t4a “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 of air resist4v tefd7)7qqab8 ed) cn 1jlk5ss;y. kda,-w oance?$\approx$    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 17502a o ;b;lqdle ruz.z n*g7,oa--W motor to lift a 315-kg piano to a sixth-story window 16.0 m aboveu;bl*la2n,zdz ae 7;.o rq-og?    s

  If a car generates 18 hp when travelin-l qes3juq-8o x;ne j.g at a steady 88km/h what must be the average force exerted on the car due to friction and air resistance?.xqql 3e-;js 8 juoe-n    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is ufdasp-9-jt:x( 8zgl nzf s/ 2the average power delivered by the e ljazstz -(pnd9/s-82u x:ffgngine?$\approx$    hp

  (a) Show that one Britis9 aiog;4pe.iyf kfw9 .h 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 - p . ngtujxaj-k6 logl*;og(;in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows - bpjs3 p-7j.6foke zzdown from to 65km/h in about 6.0 s on the level when it p f -7z6pkejbs-z3jo .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 do in 1.0 f79 y aczw21j gty3ip0h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot )ca4njuh rvnro/t:c*v:5 r. y from rest to 14m/s If this motion takes 1.5 s, what average power wac: r.ajnvy rnv* /: rh4o)ct5us developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heighc1j t ,-0yac2qtdhc*r t of 3.60 m. What output rating (watts) should cr,20q*cctjh 1t-da y the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium s *q:z,utc0sut6t v*x xtairs in 66 s. The stairs are 140 m long and inclinedt:qzxucs06,*xtu v *t 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:f yu hyvnhg1fqd u12g4/1 zs7 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 outi duzd-y 70h,jput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the d,j-i 0z7ydhu frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 31 px-h 0g*,fbrl0-kg box along a level floor at a speed of 1.2m/s ixrg -fp0*blh,f the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a vo*-lcy:lli 8jo5 1be7.0 $^{\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) bhq4 ka 4n4ppxu4e+f n.umpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bu 4 upaefn4h p+qx4.nk4mper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf fhueig,yk::) 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 b:iky:uegf )h, ook has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famousily ajal,x9w/3p1k7w long jump (Fig. 6–42) in the 1936 Olympics shows that his, 1aj iy3lxp97wwl ka/ 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 traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without f *dj.u x8a98s dmij*ukhl)r; priction along the looped track shown in Fig. 6 8l p9)jrdukdhux;m *sa.ij*8–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fel-7(zywc nry q2l 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assumyr z-y(7cwq2ning 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 enylcfb1wrlq *4q ,,;szd is fixed (Fig. 6–43)*z cb1 sl,,qlqy;fwr4 .
(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 mis ezdc 9b(o;/ountain. The climb is made in 5csdb/e;9 z i(o.0 h starting 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 ay nfssl lz1 *cm4b8+*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 Californ pd2t -w1xjbi-ia claims that its lifts can move 47,000 people per hour. If the average -jxb1id2pwt- lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 65aivjq 5ri66 kn o g69d5f sx02pyw3aq+0kg/s and falls vertically 81 m before striking wq53k+o ia ijdr65n2 apgx0fv9 y6 s6qthe turbine 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 vertica* ,l mckay:0het cw,o)l loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer dmk)yatl:cw,e coh0*,oesn’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 jr(5xh k-ha 7pb(k x9jbar directly into work, how high could an 82-kg man climb a ladder if he werea(x h- h9br(kjpj75x k 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 pfl1pb9feh hz :pkl*(-o5af 8fx jn;.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 insideiwuhi 2ctl/(/t(2 /g r)mzsyxtc)6sf the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a heighyrcius 6(htt2/ 2 t))wcm ilzf/g/sx(t of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swinj8jp voy+v)e9gs out over a lake (Fig. 6–45). He releasejyov vp8je 9+)s 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 ;g hyi;o *em) poa- -h:6rae6a)wcjwu climbs a vertical distance of 5.0 m in 9.0 s. What minimum poaoemaw a:*-g;ehpriyoc6j w- h ;u)6)wer output was used to accomplish this feat?    W

  Some electric-power companies use water to store enerdr //qw-/dt u6 1gog0ftd *y0o4zm ttxgy. Water is pumped by reversible turbine pumps from a low to a high reservoir.0zo rxod*-qdd ytt t/g//4t1m0 uf6wg 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 the spring woo;qdp5r25;4x63i xr jz iwmstiffness constant fori ;oq35jpw xdz;xw 2m56o 4irr each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m6uys d( :hy62w aj8f)-fiybjh up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h k uq+ u89s3igw, xwmv7in 3.2 s, how long will it take gqkx7m8wisuu,w 93 v +to 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 “st: hc xw6iq ;t,k:)mt6x:*c r8yfjcrqrress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimateq6ct fr:h6y:c k,i8*xxmrq j;t): w rc the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanc+9 qhvf lr0/ha-:chzke of 500 m, what was its velocity when itv:k hrzhc- qhafl0+9 / 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 w u 4 epefek0/ur6z5ue) 6p*v.slyt-ffrom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to pro60e*pupfu.l-/k5t)vezey sf rw 46 euvide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s