In what ways is the word “work” ar ,w(oqp;t)i o,bvx;fs used in everyday language the same as that defined in physics? In what ways is it different? Give e ov, x ;tbpo)f;w(,iqrxamples of both.

Can a centripetal force ever do-.q7ow a43w: vv z.oay0dkx lu work on an object? Explain.

Can the normal force on an objef*:a mtuy/ t tf+1qab7ct ever do work? Explain.

A woman swimming upstream is nothu db08,tpn5f;i/ p px moving with respect to the shore. Is she doing any work? If she stops swi0p ptp,id f8;5/ nubxhmming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cwz5oo9 pis .xr+toy1 )onsider what happens to the dishes when you pull 9pi.x zrswto y1 )5o+oa tablecloth out from under them.]

Why is it tiring to push hard aga5hedbe :*j. whinst a solid wall even though you are doing no e *eb5.jdhhw:work?

You have two springs that are identical except that spring l cwms8j.gg4 v 2is stiffer than spring 2 8smjwc4gg 2 v.$(k_1>k_2).$ 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 ;xi6,y2 tzupqefe8j4 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 ze;fu 24qy8,p6ejix ttime 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 gravitatio(bddo;2s spx *nal potential energy change when you jump aspxs;bo2ds* ( d high as you can?

In Fig. 6–31, water balloons are to;yab(, praa-g ssed from the roof of a building, all with the same speed but with different lau(pby g;a,- aranch 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 its lowes9(.)1 n,iq ocuh vtgrkt point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largestvkr9nh)oigt(uc1., q angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a 4b +c9hp natp3r6k l:wtable. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, usihk 946pc3pwlta nb:+rng the law of conservation of energy.

A bowling ball is hung from the ceiling by affe(5ywm95 zejt i, +f steel 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 supposed to release the ball without pushing it. (ij,+fw f zmte 95f5eyWhy?

What happens to the gravitational potential energyu*3 ,ligqujd: when water at the top of a waterfall falls to the pool belowu,*du gl:3ji q?

Describe the energy transformations when a child hops around on a pogo sti jvydo*d +fy8jq 7dp;4kdu05 d .+xzpqck.

Describe the energy transformations that t;p kp(c m4elpn:l)b ,jake place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrifn;4kp(lej,l: pcm p b)t.

A child on a sled (total zf 6q 9v8jfy;omass m) starts from rest at the top of a hill of height h and slides fj9qzy f6o;8vdown. 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 (. i lc kiiet9g/jwp:/over a fallen log in their path rather than stepping on top and jumping down ilc/ijw:ei. / kg9tp (on the other side. Explain.

Two identical arrows, one with io v94 3si qc pn.anujghe0(m.lb e:**twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster nie h9.cl.np:3eau q siv4(o b*m*0jgarrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energmm 7 +m;8uwru3bhv. xuy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be woun8uu7ub;vmx wm.+h3rm d up.

When a “superball” is dropped, can it rebound to a height greater than ./u3sbgwn )fv/;sf2; t )0ubkkwd efxits original height? exvfbsw )/fkbdkg u.3s2n;0 ;)f/wtuExplain.

Suppose you lift a suitcvy:6d8dil+y jt :do m3ase from the floor to a table. The work you do on the suitcase depends 8ydm +ydljdt:v6oi :3 on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the po-iz malsy gh/ 6gj7a(cra865ti mk30gwer needed rather than the work.

Why is it easier to climb a mountain via ndp 1y8)y.w5fa6n7vam d x- ala zigzag trail than to climb straight upa-1y.dl 6 )p dxw5y 7mfavann8?

Recall from Chapter 4, Example 4–14, that you can use a p:7k-ic( ttsf/c b u;axulley and ropes to decrease the force needed to raise a heavy load (see Figtku t/; acf7 xs-:b(ic. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by:x 5m, 6l.+zfzfk acmn the gravitational force when a 265-kg pile driver falls 2.80 m? a 6: k.mfzm 5+xlcznf,   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much worjepn+ t;xir try;a-pr;-cc + 5k is requirex- r5prjtnp;ce+c -;;yairt+ d?    J

  A 1300-N crate rests on the floor. How much work is reqg7gb hujb9 a(4d 0ch)suired to move it at constant speed (a) 4.0 m along the floor against a fri9duhbh () bc7 0sga4gjction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg cratecw8 (k8/ain ok 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50? (/ocnk i kw88a   J

  A box of mass 5.0 kg i t vp8c3zi6gy2s accelerated by a force across a floor at a rate of for 7.0 s. Find the net work done 82ip gz6 3vtycon the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on/udokwuow2w/c8u; h:ro(u1dx8 xly *9 w7 xo p a table. How much work is required to stack them one on top of anothercx/(d/u7ux8 x uwr1h lw yo od;ko:29*o8wpwu?    J

A lever such as that shown in Fig. 6-35 can be used to lifc0if87knk6 +t5fz5jeiokdv0/bh r-q f objects we might not otherwise be able ton 0qzkj +ev/ 7 -fdf5b cik56hktri08o liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 8xoghi0 i-o wnl 5g,r/c hb:r63.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectirh,0 g85:/clwx-roh 6iin b ogve 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 h yqa(qr e5;fzv)j h(2belicopter of mass M an acceleration of 0.10 g upward. ) ;yf(aevr2qbzhq5( j    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 axisu0p sue -zvzh9* ul/6k 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, zf t55ntvw+ 9 u/ 6vjnw)3svxrvaries as shown in Fig. 6–37. Determine the work done by this force to move the object )wjt u+5nw9nv6v5f / 3zrsvtx(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 exerte4h e i3dhh.n9 tuk(+wdd on a particle 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 mass of r+2t1nh*b kj x$5.31\times10^{-26}$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, b z ,v)erodn: 758s/fpc6 nmi:xwdd m2hy what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elecch,3 vzn2u9e rtron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 donb65c.du7 *svemp f+yl e to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average f) ykh 54a5/yjmnjb egsr5p0zfn+7lb/ orce of 110 N on the arrow over a de)5mgy7 z4bsyhl/0r5pkbjnn+ j a5/ fistance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelipfzii/:kf:3 gfi6 /go le(b6z ng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. Whaibeffig3 /pzlkiz ( :gf6 o/:6t 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 brar;0 vx zlr4fv at, ln.xu6ud,+king distance be dlu0 ;+xnaf. vv6rx, ,zu lt4rincreased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a l:a)d unmn5lh)o1i )l; 7h+wqyk(vn jrevel 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) the brakes. (Why does to;n h)qniw)ku)5j+(hd 7rly1: alvn mhe car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches the :;uhsx6 iq5 caqn.6f wplate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resista;5ah w.nx u:6cq fqis6nce 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 up by someone who 1.e jnik8+ rw)0nmm p05xqtrbhz1ek4does 80.0 J of +h. kr )8np5n iqe 1jr1 kbt00mmz4ewxwork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratio .e b,eg8p7 iunk-fya3n by a single cable. Depbgn.u,e i 73-e afk8ytermine
(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 must t6 zr::tr ,xivbhis spring be stretched to store 25 Jvi ,6rbzx:t:r of potential energy?    m

  A 7.0-kg monkey swing x3qy 7tf 5ld92qrmmu0s from one branch to another 1.2 m higher. What is the change in potential energm tlq0qm9f 5273udxryy?    J

  By how much does the gravitational pot4 r6 m/p dgc0xy5ti 5xbtuj**nential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m 0gdbi txcy* un/px r45m6j *t5during the jump?    J

  A 1200-kg car rolling on aiv y6,/c4(icgbdvxw + horizontal surface has speed v = 65 km/h when it strikes a horizontc6,wv v(id +cx/ by4gial coiled 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 x-:+lazwg j.mn+1f pz.10-kg book from the ground so it is 2.20 m above the groun nzpxa+wgj .lm+zf 1:-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 elevation of 1600 m anv ;efzc9o6 wxjp(01w+.p gne bd climbs to the top of a 3300-m jcxp0 +f 6;wev.o (w91bgnpezpeak.
(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. Tm j5 vue4ein o(tl3bzv)s*;1z*aoqql8lf *k6 he end of the spring 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, wh;q*esqv43*)l u zlo(n e61kb58 mv flia*jzotere will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runni8en lo6 vo,b7bng at top speed (5.3m/s) and grabs a vine hanging vert ,on o6v7elb8bically 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 down a0u3 +/te imo* tiyvjr,8jkty-o +:i85xuisx o 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 qvd md1;rsd xr:cef- y;n6c-2shove 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 transforme6v/+p (cthsm kg4xn3 od 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 ma4/konhv g6s(x 3c+tpmss 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 the top ofw76a*uchl.8uvs bj6n a platform with a speed of l j*6.cuh7wv b6 unas85.0 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 itse2 3eovz g13hwjh m:2yxg9 ze7 mass), whose spring stiffness constant is 950N/m is attached to a tzjhy1zge2 mx w23 3ve9go: 7heable and is compressed down 0.150 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 :fl k m;p0wk xt fk-/x59a0noqwithout friction along the looped track shown in Fig. 6–39. If the block is to remain on the tnk atp9-f0:5/k xxmqkfl w0;orack, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stifsr, vlsr5f9-t 0 *tl 1popjr;vfness constant k), Fig. 6–40. The bl,rol r *pvs9s p5;vt tf0r1-ljock 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 tiedy;l0ni: f* arl to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the sprin0;: lnlya *rfig 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 pxo:l5cr-pc m) oint 1 where it is released from rest. Assuming no friction, calculatex)p 5:lmcco r- the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 sfuob-m76rpbb+ kv;5 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 bottom of an elh8)q,g q4fgbr2mex 73dx2 w syevator shaft. If the elevator cable should bgdr42 xg8f )sw bmhex7 3qy2,qreak 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 upzse l)0 u4m7na a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite direc x0z slc)j,fi+tions,i)0+jz x slcf, collide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descewk;6v; a, pi+xhsue2yhs2)vp nds a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy ;hy6ip ,sv)hu+x ap w2;evsk2 due to friction was generated in this process?    J

  A ski starts from rest and slix ncsg,gn y6*pn*jxkv/n m(6r a/, q6sdes 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 groundo.q c67moyexf.6cf5 s .
(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 boujf*tja) a x/*hoz6sa( co)g f8nces back to a height of 1.5 m8*ao) *6 gft/ zcsjjafhxao )(.
(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 with a oqmwos :/tfi4;g s i:d7wc/e2constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the:/s;2m:qwfgedos7cii o/ t4 w 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,ykei3e6qtck x2 s7f) point 1 with a speed of If the averagext,s)7q23efy e ck6ki force of 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 steady upward 18.s)/hpn ,wfmuu yp60; e0 $^{\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 horizontaljfsd)oy2 5sd-rs q8 c( spring (k=180Ncfq2rysd5s oj )sd(8-/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spri ke:d2l;xi6mj-kh6 )ryz n d.qng, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 2yzrj-2h ) 6en6 qddl;k.mixk:2 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 “glider” (mass of 98 .(.mh 4f4ps6pdseehviva0)t 0 kg including pilot) that was launched horizontalm.t64sp h. (h)ef 4vsvi0pa dely 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 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 3lec1 jw,:oca3p:wjd sr51zf9v( u dfmotor to lift a 315-kg piano to a sixth-story window 16.d3d(1vfu:51 oepcjw jf3 lrwa csz,:9 0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h6cit+27kw cwyh y w.3k what must be the average force exerted on the carc +6wkw7tiykhw.3 c2 y due to friction and air resistance?    N

  A 1400-kg sports car: 4q9 ry;ok5sf lzihsq51q( yq accelerates from rest to 95km/h in 7.4 s. What is the average power delivered b5sf(lq4;ir qy9k1 qh qsy5oz:y the engine?$\approx$    hp

  (a) Show that one British hor3f1oomtt*+ jvzlx 359x a p*fosepower$ \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 the form of9h 5l4u4ufoa:x+ romp “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 fro: , z3i3qr e1 elg,8ihvcyzoq.yov1(u m 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 cyge:8 qo,uei vlz13royvci( z,. 3qh1 ar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do ml9j-lvr3 a zjdm8) cnd,,*ea in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion t15o mbazg4 m(gk 1ff/ 5o0rmbxakes 1.5 s, what average powrz gf1a0oo f (5mmbb51mx /k4ger was developed?$\approx$    W

  A pump is to lift 18.0 kg of water perbnq/ c6g9i(xt+ ) bn1 qxb0xcl minute through a height of 3.60 m. What output rating (watts) should the pump mb( / q1ixxtcbx) l0c+bgn 96qnotor have?    W

  During a workout, the footba rp/qdimeq 0b9 e7a(e,ll players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long andbeaq(eq ,rm7i90epd/ 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 cdlr u:3 y)f3f w /r1.aym klc21aqbx*$^{\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 u7) -zowi q)krhp. How steep a hill can it climb) -rwiokuzq )7 at a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor acm5kll 465 pql6jo) /xl2h. jxtq+ i,cgogl1have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient lcl+h/x o.)l6lj5 lqt4qg g1a2ixmkc j5,op6of friction is 0.45?    hp

  A bicyclist coasts down a 7xq:5*x9 y btdv.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 hot:a x8q e pz(o-*jw 9t6yhgu /jl;v0yave 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 a ( ogt:-u0hw6 z;t/o lvxyyjap e89j*qfter a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first x2p ew 4l1t7*nkusf1 l2ke rr*w1ky2r shelf is 10.0 cm off the ground, and the remaining four shelves are lrfwet *1sl knpre21k*k7 2uwy4 12xr 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 all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’stg 011wma2op5z xxp t8 famous long jump (Fig. 6–42) in the 1936 Olympics shows that his cp pz2t05wmxx1 atgo81enter 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 frf65-al.;mbo sdolsh + 0umhl6iction along the looped track shown in Fig. 6–39 is to remain on the track at all timess0 6+mo.5-hm;lb6 l udhlaso f, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircidbz56a 8rt: /ieej .1 kok7xwraft without his parachute openio1iae68k5k.zdx/bi jt r7w:eng. 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 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 enri8ibp ,g.vj 5j9s:p dd is fixed (Fig,:d sj.v g9rp b5iij8p. 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 ez 9/2y g/)bi izahp0ftop of a 3700-m-high mountain. The climb is made in 5.0 h starting at an2a/gbp/fi i y0 ze9hz) 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 elqr7 3-awlkd 5eevator 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 peopme,64sul03(c x sebakle per hour. If the average li4,l(6 0k3c xs aesbemuft carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the ratjrhi.b d j) :v73k4euie of 650kg/s and falls vertically 81 m before striking r ibjhu)i vk4:j 7d3.ethe 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 vertical loop (Fig. 6–44), the- ke1ziq*+b+ xnqiuq. 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 iu+n zbxi-qq .ek*+i q1s 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 work, how high co /sr 9*hu7t3g)qnhx ge.,aekould an 82-kg man climb a lak,eg ge9xhtqnush .o)7a*r/3 dder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of jnr;,toa4wwqa 1 d2l ,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 bathrm w per:oa/:(joom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now j/eomr :a p:(wif you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over iq -ofd j3ea14)7u utzgu8fl)a lake (Fig. 6–45). He reou)lfafj) tigzuq 478d1 e-u3leases 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 dist m9obv9k :3u vnh aq,gu6s8e bzea(q(6ance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this 89bneau( 6zv, hu o(b:sgmqkeq 6v39afeat?    W

  Some electric-power companies use water to 1y7fx9vmj 8wvswl/3f store energy. Water is pumped by reversible turbine pumps from a low tvl/ yfw 31 mfjws97vx8o a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constans8n,r2aprks;0t8r q it k is cut in half. What is the spring stiffness constant for each of the two resulting sprpr,2sran; q88ikr st0ings?   k

  A 6.0-kg block is pushedy8 ugyxfqfg5z (bo9sv6f9/3 g 8.0 m 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:.t*b y1vzoy o 55km/h in 3.2 s, how long will it take to accelerate from zvty*:bo.1o y 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”),,.ds0r )ct 2;i 4hf9tdgvcen4m4vv bg the patient walks on an in).r9dhet mgcdg042 tcv b4 fvin4v s,;clined 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 verticalvwb :g s9(b.srxp-b7bly upward a distance of 500 m, what was its velocity when it left the vol 7-(wgb:b9xr.sbps vb cano? $\approx$    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) .kf:.sk-fwj pIf this water wheel is set up to provide electricity output, what is its maximum powes. .wjk k:ffp-r output?    W
(b) What is the speed of the water as it hits the wheel?    m/s