In what ways is the word “work” as used in everyday language the same as th kkp.s3 dbbv15at defined in vbp s13kdk.5b physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an uey9p s;c 2u-bobject? Explain.

Can the normal force nbwlgf0r k 48b 6ea y4b8qwq::on an object ever do work? Explain.

A woman swimming upstream is not mov2 j*;rdee5n2 (il uqnling with respect to the shore. Is she doing any wo*nleierldjqu n5;2 2 (rk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hinb/gnf85zu m 0ut: Consider what happens to the dishes when you pulfn5 08mgu ubz/l a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing nop:bnakx,mb 47 w7mbx4pkna:, bork?

You have two springs that are identical 2w 52s5kwlhgbexcept that spring l is stiffer than spring 2 lbs2whkw25 g 5$(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slidph(o/gpqx:m /zd-p ghz6ag gzy18) 8w e on a frictionless surface (Fig.6-ydw8q6gp ohha: m(g 8zg)pz//xzp 1g-30). The block starts from rest at 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 gravit0(jscrizrars -8 f .y 1un0fv2)x.sunational potential energy change when you jump as high as0n ur r1a ssn.zvyjisc (x.u0-rf2f8) you can?

In Fig. 6–31, water balloons are tossed from the roof ofxe8g sg8 7td4a a building, all with the same speed but with die tg8d8x 47sgafferent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launchexz5z vm urd2 39ln:7ap+ 2phfwd from a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pen+z:pw f25ra3u zp7x2 h dmvn9ldulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright sr p2w0 gu:5zhx/ 7tpgt2/ wmsac8sp5 on a table. If you compress the spring by pressing down with your hand and then release it, can the spring c8/g tm s:p 2s 7pthg5w5xrp0uawzs2/leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a stev.9(+8rq d)(laah/w i s1ot hrkl:kqbel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is su) 8k w+ot(/lq qrsl9hv ihk(.dra:ba1pposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watewb ynkcqa87t ,4fg1(opll ,j/r at the top of a waterfall falls to the pooc4wg l,l ,k bf7qp8( yno/jta1l below?

Describe the energy transformations when a child hops around on6i:o8i1, q qj+bomozu a pogo stick.

Describe the energy tm pxzdp+ps-by(sx9nd,mq6oj : 07/ dfransformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snm pjysspb(60dxmdqd/ z +o9fn-x 7:,powdrift.

A child on a sled (total mass m) starts from rest at zm/ x m*y39ftfthe top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is ffy/ m 3ztxm9*icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in s.bgvd.7 ah 3xtheir path rather than stepping on s.73vgb.a hxdtop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the t.vh 50h(b zuu, zy0t4gh:rgs other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fastg0thvh(4 uy:bh5 r.z,g tuzs0er arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of5xo x1y ybodpr0;o 0h* energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatheyy; x50 rhp0* 1oboxodr clock has to be wound up.

When a “superball” is droppedo cbfq112-cs: up unx(, can it rebound to a height greater than its original height? Exp q2cfxos-(c :pb1 1uunlain.

Suppose you lift a suitcase from the floor to a table. The work you do on the sbs oy,,+p). zxanz-z jc+2hqbnb8ha .uitcase depends on which of the following: (a) whether you lift it straiq+jnn)z+8apo2cz,b .y xs-bha z.bh ,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 thep;p. r;jgoqyc2o hx+ : power needed rather than the work.

Why is it easier to c8dxg3u n cpe) u4;iyf8limb a mountain via a zigzag trail than to climb straight up)y 88pfe g;dn4iucux 3?

Recall from Chapter 4, Example g7.* )rd czgbw4–14, that you 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 mu wr*b 7zcg.)dgst be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fal/i( aol cks2:bxrg 1rt 5l:fe(ls fg2bt(:(1 lre:oci 5sra/ lk x2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hig qjh*3ns v37nrh. How much work is required?n r7 3vjn3shq*    J

  A 1300-N crate rests on the floor. How much work is required to move it atw kv 82r(:afq5wvzsr) constant speed (a) 4.0 m along thevrvz25k(:a)wq wsr 8 f floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (ho mdxc 6c;hk)55a mph5,ky ,+c sooa)gorizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coef)hm5oc g6p ;o,mxc o5h s,ay a+)5kdckficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flootk)2ulqasosd7z o//lbn7 3); qnoxc0 r at a rate of for 7.0 s. Find the net work done on the box. b)s3k2cl7 ol;qodn st0uzn //xao)7q   J

  Eight books, each 4.3 cm thick witmmp y:6*o sg-mh mass 1.7 kg, lie flat on a table. How much work is required :ogs*m6py m-mto stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects w1f9rcihvam 5*. ;my de0lqyr5e might not otherwise be able to liff. 5q*9ic .e5mlry 0y vdhm;1afr 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 21:m x1wrzqs6vija z, us h0;2x8° incline and is kept from accelerating by a man who is ;16xxrm ah0qwzv1s2: zijus, pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mi2f2r79zi t6;y0fas m 1;mzlvld + :objjeyb1ass M an acceleration of 0.10:2 ;j aei l6d;rfzo9msjz 2y +11ifbby7tvlm0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distanc )7h1bjh6knlgu e3hw;e 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 wb r)wmx3u6g lp7/fh7b6 v 3,v,fyadfalong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10ghu) 6y3,x7 6mw/fafb,v7 fd3wbvlrp 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 parqyddu6 9t m0fzd7::ow ticle 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,nsyv7) a64s hg 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 a0c+cfbm6ah sff +qz(t-r 3s 4doubled, 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 tdqs:i0 +ljqg,4 y z)ito 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 -dus7xr,udmn fp; 53 92orkd;-qpgge 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a 4fk /9 bmbzmc5bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of t mfzc5m4bb9/khe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwarhxz i7)43+avelcmzt89 y-xja:t afs2 d 25 cm when the ball isz 8ea2)c:j3f aivy+t tmxh9 -s7xzl 4a 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 what factor will its minimum be ;aqnq ys (gqmr*0s(m9j3: cqraking distance be increased, assuming all else is the 3 :n9qj gamqyme(;ss0q(crq * same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark ti ;wes cady0 ljxw)0: v07 tlk,ui6jj6o be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic fj eiv0ka ,:wxd6j6j0uic7 wtys0; l )lriction 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 at By l3)cd.1dbkbz the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pb3z.lkcb d)1ditcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight uex1 9* pv:qfsj1ke4 (dg f)r ff5gecf:p by someone who does 80.0 J of work on it? Neglect air resi1sxfjcred5eg(e :qf:v9)1pf 4 fgk*fstance.    m

  A 285-kg load is lifted 22.0 m vertically with w:,. gj2jak cran acceleration by a single cable. Determi rj w:a2,kcj.gne
(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 constafc8e, ay2k7uznt, k, of 440N/m How much must this spring be stretched to skfy,7uz e 8a2ctore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. q.8yzi btrn+4 o epi1d( lmyk8.-sx5tWhat is the change in potential+oexm8zn8k5 tq.ti-yyl.d 4p i(s r b1 energy?    J

  By how much does the gravitational potend ,kz,h ik:bj;ug+ap*tial energy of a 64-kg pole vaulter change if his k: ,+u; az*b,dihgkjp center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sithy31/ yp7kvtitenlco;1hjl7 r 607urface has speed v = 65 km/h when it strikes a horizontal coil0lc /37i;lnjpikhyt 7o11r eytvt 76hed spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is v0f kvhwf5 h7+2.20 m above the gr whv+05ff kvh7ound. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of 60i: zd.ly x.6xh.r. is1rwllxbmns7 a 3300-m p6ss1zbri.7 hxy0l.: l m6xwrxil.n .d eak.
(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 verf0bk5;+(l w/3gfqvfjzkl8 to tically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If kb 5 zg;3jl/qltf 8fvwk(fo0+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 (5.38elu)w4 q9*xiak)esg im*a 2rm/s) and grabs a vine hanging vertically from a tall tmkii*l e qs ex)84r2 9waua*g)ree 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 3/qz(cwk: 0i:b g) wdqkv nk0jfrom rest, slides 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 bt8)/eug9btuf-3p hq given a shove 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 gravitatk/nb jq//7u3ax w, xtzional 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 bar with nqzubk3/wtxjx, 7/a / a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of ajv*4gu,kbifd /5ch0su7r zw u9ik .j; platform with w, v. zk;ik ubif/ds ruhcu*07g5j9j4a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant isjrt15*rtmn- v5xg 1 pn 950N/m is attached to a table and is compressed down 0.150r51 *xpr-nt1mt 5jvn g m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown ihfw-9 cab;nzqn -1 i-xn 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 mn fn-z1b;- axic9qh-wust it be released?    r

A block of mass m is att* :l3chnuzs/qquyw t)qu96p.wi *9ssached to the end of a spring (spring stiffness constant k), Fig. 6–40. The l6cwp. 9w usz3s*sutuqn y9q)/*i: hq 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 t wab1z x h1bh ,;)rkum2b6yp+hied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m.k hwyxh6z2+1);a1m u,r b bpbh (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 drshag*aal u i yj2z2/31agged up to point 1 where it is released from g iu/alzs*y jaah23 21rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 122ng 9c;h: drim 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 placed at the w0 4yrtj5i 2dea2y1j1e2 iorw bottom of an elevator shaftw1er2j0rj52yo e1wd4y2at i i. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up vw hfy( dg84)za 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 lt(+ jl ;k/wesof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest.l/js+w kl;t (e 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 bottom wv 9o9fb;*h44utxp tw lith a speed of 2.2m/s How much thermal energy due to frl;hp *o vfwb4t9x4t9u iction was generated in this process?    J

  A ski starts from reoahs -gph 8g.+st and slides 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 k3mwl306jurf)3 h5i qr7vwzltree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5 m/3m c+gue .7kz kj,jij.7k,egu/ 3+c mjkjzji.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor wit ;38zajrxls 3+k ,kx6z) d++6 f d4iazgqtqaneh 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 friction is 0.30. What is the final spee663+zsdftkaj;x z)a4 xnr8gdkqa ,3zi el++qd of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a st 7ru/jbfy:*g kok :msgyu5,4peed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poinm/57y ku f4sy:rjg *ukb ,got:t 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s w;3, rjep; 4 mxwey9threaches the 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 blockfe s an 7;;fs/,wcl-la is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before7lc;f afsl ,wen/a-;s stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is fi,l)(itz hkf5 rrmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far z5, )k(ifl rhtbeyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “cos; pk)mw/j9 glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height pow/) 9csmj;k 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 resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to l- ;:ta,:nu8om1p :shk qcxbza sixth-story window 16.0 uzl qxt h 8s:a:b1n:;-mk,pco m above?    s

  If a car generates 18 hp 57ugpv p)8k kzwhen traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air gzkkp8v)5 7pu resistance?    N

  A 1400-kg sports car accelerates from rest 4(2cwi epxn 5j+zm at5to 95km/h in 7.4 s. What is the average power deliv apc( zm5wj4nt5x2 e+iered by the engine?$\approx$    hp

  (a) Show that one British m5uekc1 y 1b.2yb h 3bc7o8lpehorsepower$ \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 trbzly)xp38 3k7kn; i xd,6zmehe 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 9ab zd/ uv( 4e8acydu61150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at (y ua4d9vu6/z ea c8dba constant 75km/h.    hp

  How much work can a 3.0-hp moto)e;ekr40ke wr 6wpq y:r do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/shycxox14eau7 j-1i j( If this motion takes 1.5 s, what average power was d 7xuoje-a1yh 4cx1j(ieveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What oofx/7*woh2ko tvux(80mhlg 2 utput rating (watt m72tok/huof8l v2xg hw*0x(os) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium -yvp b/p; tsw2,,xngmar.1yc stairs in 66 s. The stairs are 140 m long and inclined at cgtpx/1vay,r ,pnyw2m;bs- .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 climbww/yu tdze+bilf.f.4,m1fly)/ ) mql 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. How steep eq,dlrrh*(t2fto fucp)/q5p 6e/0sa a hill can it climb at a constant speed of 75km/h if the frictio fqpu*he(,/2l6deqop5 0rscr/at ) ftnal forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to c d*t,(ydmw(y be able to drag a 310-kg box along a level floor at a speed of 1.2m/s mwd(t*(cy y,d if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down 5*01bymts;af3e;j;txhimf v4su2 c ba 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 (j g *mhbvwsn4l7sb3 )cars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a j v7mbl)*s4wshb( ng3solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remainin)8ae(d t gqv5mg four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are )e(gtda58 mq vall laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fm7 sji88ubj ls 7o)m3big. 6–42) in the 1936 Olympics shows that his center of mass rose u8jiom)8 b77m jbsls31.1 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 s8 +:tzutppr*4ze,5k x rc7wqgliding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at ,upxt+r ztq c rpg4z k8e:7w*5the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 6im+l ebug0959 7arvkmu) ogu 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.19)095kmg+elru6 ui gmbvoau7 m deep, but survived with only minor 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 othelp- zb 16gxv)rr end is fixed (Fibz6p-gl r) 1vxg. 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 c xv4,n qof cf ap;o1v.yq982pslimb is made in 5.0 h starting at an elevation of 2300 m. Calculate x9v1 8,pnc a q oofyq2vsf.4;p
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge sprin8mhn03dw m( wsg ($k=2.2\times10^{5} \mathrm{N/m}$) 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 ttwg0+rk h+q2jx/g y 6lifts can move 47,000 people per hour. I2+rk+wg6qt /xh gy j0tf the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 8vw 3h 4(amizk1t:dp3m1 m before striking the turbine blades. Calculatekhmi 4dm: v(3z1tpaw 3
(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 ve,75h 9pwj3z p+ *;je(-jwaehemmljh yrtical 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, sy+pj w -5emw hh( m7*h9jjzeap3lj, ;eix 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 : sx2bmn bxj; *-cdt02 )qwbjqvms)f( candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by on0) :2 q;bt)fmj2q*xbwn(mxvsc b s dj-e 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 upwarir9m*ui(j .708er ge cvy8zppu/: lsfx nmn;9 d 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 inside the scale codj5u5 rh gb(b1mpresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height u jd51h5(bbr gof 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45cvrpaz 9e98:p ). He releases the rope when epzv:98 9rpachis 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 verticax k:asp -r ;cc8vw w-dwdw06lk +dar4(l distance of 5.0 m in 9.0 s. What minimum power out048wac (xwkscrawv l :kr6;d +- -dwpdput was used to accomplish this feat?    W

  Some electric-power companies use w:xg 7nhb)xa z/ater to store energy. Water is pumped by reversible turbine gxx:/7bzn ha)pumps from a low 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 5dv72ccrl z8m stiffness constant k is cut in half. What is the spring stiffness constant for each of the two resul5czl8v2 rc 7dmting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 jnw ladf,9 yl0 0c7(lt$^{\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 accelemri,b 4 +58xxsli/udl,; mfxsrate 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, l5,s4+m if;ruxs, /mxx dlbi8 and neglect frictional losses.    s

  In a common test for c::w ucqfj7 w br:i-(wtiox -8lardiac function (the “stress test”), the patient walks on an inclintw-q8 wu:wrboi:cfj7l i :- (xed treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of sq 2/vbq; gdu+500 m, what was its velocity when it left the uq; v+sdbqg/2 volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 9xxm2igll3j ,cv/4y8 l5kg/s (a) If this water wheel is set up to provide electricityl82iyjlx ,l/4 g3v cmx output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s