In what ways is the word “work” as used in everyday language the samedr3v lp)k;v3 cv ,h 03:phk/gx+upyf i as that defined in physics? In what f303; kphrlvv:x p)3i u +vdcpky,gh/ ways is it different? Give examples of both.

Can a centripetal force ever do woz6d;w.:q7z msx*-pfaor tw s- rk on an object? Explain.

Can the normal force onpod94uyv/31r a5oca j.crpd 2pi)nk* an object ever do work? Explain.

A woman swimming upstreavs; t, a3wkc:zm is not moving with respect to the shore. Is she doing any work? If she stops c:k;3tv aw, szswimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider ,*rj-zyt4 (eg my1twye,l vw-what happens to the dishes when you pull a tablecloth out f4el-,zmy,wg t r-y t 1vyew(*jrom under them.]

Why is it tiring to push hard againsx kwk8c1 1.gtht a solid wall even though you are doing no 1.1c8xth kgkwwork?

You have two springsakgv / +9tdl-nx,dmcfw0ul- 9 that are identical except that spring l is stiffer than spr-0l9 l/fk +-ndwg, 9md ucvxtaing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a eom: v sdk)-fxxc51 )orx9ef: block that is free to slide on a frictionless surface (Fig.6-30). The block staedk:o-fve 19 cr)sxx5)of x:mrts 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 yourau; c4auhbwf66;) d hhq/is(v gravitational potential energy change when you jump ashquhwh av/);6u f;ci(ba4 sd6 high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with th -4frr* 8dlldh;/a cswe same speed but with8*;dw 4chl ar rlsd/-f different launch 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 lowest qu kkl7h /8.kfpoint 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 8ku 7klqfh/.kinitial 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 5c ewd4u 6eo4d jf ;mk vwb,.s:k+3frmupright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring lk46m be,m54osdw e3fr:;fj vdkwu+. ceave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceilin/n*2vg9/0 cjru zhrgvg by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands again2c *hvgrr9 0vguz nj//st the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wa( b1t.t tip 8vx6y6yvjter at the top of a waterfall falls it(bjv6 vy1.txy6pt8 to the pool below?

Describe the energy transformations when a child hops arouo-e1:wc-aiu iy4wj u -nd on a pogo stick.

Describe the energy transformations that take place when a skier stx;i u3 a- *f0 +b8lun8,o8fikaypnaerarts skiing down a hill, but after a time is brought to rest by striking a o fu8y-0k p3ani8*a,iaxf +bne; r8lusnowdrift.

A child on a sled (total mass m) k;8hbl na,- s vize.gwx4j0;nstarts from rest at the top of a hill of height h and slides down. Does the velocity at the botto le.0vxwnk isjbag;;h, z 84n-m 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 over a fallen log in their path rather than steppu.ig u;90umi ad8qcz4z 2uz) ging c .mqi0)a2igzzuu ;uu9gz84d on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the ot e95:oxvryq 2kqes)ywyz+*dl-g-b5 j her, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetratw b2o9gy5z: r*ey qlj+v y-5xq)-kes de how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms ofy5rzsi7xu2n8 tk6o y3 energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandsyo5zur3x6n i 2y78 tkfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gr8::rtkf;d(l ,o0uhyfr 8 s .yzsxw ,hceater than its original height? Explahwl,:szr f yh0you(k8 .: dt8f ;xrs,cin.

Suppose you lift a suitcase from the floor to a tabl6nrwa+s wpe9fgvnq7 3ad *u vb7/ m-*be. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcsvrvab 3n7q /ae wgfb6-w9d7m+npu** ase?

Repeat Question 22 for the power:fgv:, :wsc 6.iq4h8xsrz z ox needed rather than the work.

Why is it easier to climb awe1dy(;.tapy: ni)kh mountain via a zigzag trail than to climb straight un1 yt.yk(h: a);dpi wep?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to decn56ad dax:bs+dma+4vh /qi : d.rvrt5rease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much ropea / m. nr::v+i ddt+hb5d a56vsq4ardx must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationat e*cjq7 64yx6ogn 5qcngr)e1l force when a 265-kg pile driver falls 2.n7 )gcg*1eqr56xj cyt ne 64oq80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. 2 xvq9k,nkw1nHow much work is requi9nxwk2 v,1 kqnred?    J

  A 1300-N crate rests on the floor. How much work is 8 h+ig pdxb)tqw+n n z6h+uf,6(z v7gcxj-px8required to move it at constant speed (a) 4.0 m aunq)7 c xn+6xtp-dh g+( wx f6z,8jgiz+bhp 8vlong the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizon.qual qw,4 5bltally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effullabw .qq,45 ective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accrk78fm3z vi3 eelerated by a force across a floor at a rate of for 7.0 s.38 7irzv f3ekm Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 k) f nas 0,s8n1nzpahc7g, lie flat on a table. How much work is required to stack them one on n za)c,ah 1nps87nf0stop of another?    J

A lever such as that shown in Fig. 6-35 can be)v6igk,li + 2xea apbwt1 y-vkg(:st( used to liff objects we might not otherwise b t )p lvgb-(k:2gakwvxy i6ai,+(se1te able to 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 3.6 m down a 28° incline and is kept from accelerauf1oie0 lzih qx, iad+g: 11dp- 9*fvnting by a man who is pushing back onadlo,iu1pxdf1 9 z0 *qev:-1g in fih+ 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 mass M an acceleratmh643kd we9o cion of 0.10 g upward6cwohem3 9 4dk.    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 is l ic3q4;amio z,inear 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, varies ash 2re h;izskx-qurvfxgov (9m0i,.h /+s -.ax shown in Fig. 6–37. Determine -0akum ;vsg h i xxr/ih fqrh(seo,.+.x9v -z2the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerte9c(5 ,ox pt.qbd/jq t ;+sr7k vky2miqd 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 o t,nmd)9ya au/xygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor 8zp.) uyxsa 6x5c0ydowk(b1w has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requ35tx-a3nb :i)unt *(u efbws sired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar travelin; 3ei onuiy-v,+d ru,m,shw f3g at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firenlx-*wa0uc n6 d from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a0w *l nc6uxn-as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwardf;g,z,hb.8w-,s wn :ikpopmuw, pb)t 25 cm when the ball is caught. What was the average force exerted by the :f,mp.p,b o-gp,wtbk;) s,w8 inzhuw ball on the glove?    N

If the speed of a cat9 r)+)c7mo o wv7 waribuvl rzv.31,cr is increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the l orcwv7.3ocw 7v))vuzmr itar,+b 91 same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’su9o*.ovgqtj m/:dz -hmkr:2 q skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic fritu2*z rq qk m/ho: :-ojv.mg9dction 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 kga stcwg;8i p ;j/*wfr9 is pitched at By the time it reaches the plate, it may have slowed by 10%. Ne;tjws 8;9paci gw */frglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by some,3lety omc;k 6 k4rw2eone who does 80.0 J of work on it? Neg; o e2k6 yck3mrltew4,lect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singl 17ryfw8gsl m;e cable 7;y8r lfm1gws. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring6 *lijn- mspp h/3,ipk stiffness constant, k, of 440N/m How much must this spring be stretched to store 2-p sjnph ,l/36iikp *m5 J of potential energy?    m

  A 7.0-kg monkey swings from 1:p2mp m5e g,l)tz*nm8 mjz-x1jxmsvone branch to another 1.2 m higher. What is the change m,j8tl 1-xsj m2n z1mm*p pvz5x):emg in potential energy?    J

  By how much does the gravitational khj/bd;s*).lk dkx-2,w wt yn-y msl-vc(kt.potential energy of a 64-kg pole vaulter change if v *tl-lb/n,tm ykkk-h-scj w) d(; sw.y.xd 2khis center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontaly0f bj;v je;k. surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring fy0v j;k.bj; estiffness 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 m2c 2s c y;tv4hho2vk2r above the ground. What is the potential enercvs2 c;h2r2 vht oky24gy 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 a 3300-msic o-oeg: 0w8 : 0h(fple+z7xhaqpt, peakxq(h pof,ee h:a+ ilsz8 - cwpgot007:.
(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 sprn:/ g/;psxa7rm 5vk-qkyon* qing is next t75/prn/n aok mg ;q*syqvkx:-o the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spewty 25(m8bd *yucb9 e;:cy (tdv8c xzwed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she st2*e dwd9wc t(y yx5um(8cv;bczb 8:ywing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a fri*dx2enb bim7d8 gn85g. jqu ,gym5tk4ctionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up axao xjtv) n(;1 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 kwsg184lu1 gh1px ) ) gn*tvyzcinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the 114h lv)c tg)wggx*unz 1s8y pground 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 the top ofb+rhoy4 g61rm a platform with a speed ofgro+ hybr46m1 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 stiffn9s av8p7l36e nx3gf kf 1go2gxess constant is 950N/m is attached to a tablg6 3lpfxg 1anv9s3k78ofgx 2ee 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 without friction along the looped tra.f 5a fdf:4syick shown in Fig. 6–39. If the block is to remain : sfyif45df.aon the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached 8.kipbqf ) :bw l7ct6xto the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displac: 8f6lc.7kw) iqbtpxbement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose u1vam a74vag y*fh92yanstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k ofv a aga21vhfayym47 9* 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 v,aw qg8 po1dait328mto point 1 where it is released from rest. Assuming no friction, calculate the speed at pida8m ,vwq 13 gatop82oints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/n3z u9 jo-izv7s 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 /f:as0e 2bi5tn ,(qtqblhy , kbe placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a eil, yhb q0/ tqb2ka, sf(5nt: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 d xfen03b;/f.p)qa ,bc4v gch 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 travfby* ( ykp me86+s+/ymgy ch9feling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is producedcgmy*6 (8+/y9 ypeffy+ kb hsm 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 wihg0hbxopm*o; f.3dm k lu 4z),th a speed of 2.2m/s How much thermal energy duh* l;o udk3,zb4f.p0mx hog )me to friction was generated in this process?    J

  A ski starts from rest and slides dojoui3o y+a 5c uj45*zwwn 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 d*y *,0igoj1 yx-)pipz3htdyoropped from a tree 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:gz(c08gby y fnz 5 5pt;2enru.0 m, and it bounces back to a height of 1.5 m 0:8g5bc;5(zern tfygypnuz2 .
(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 ai mpc6d704gn e constant horizontal force of 350 N. For the first 15 m the floo6ne4pcg 7dm 0ir is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coal,:t3 by,gxnl ster in Fig. 6–41 passes point 1 with a speed of If the average 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,lx,3 n gbly:t m. $\approx$    m/s

  A skier traveling 12m/s reaches tj9 p3/izdhx..conud h9:rz (ehe 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 horizonth(u rb sqma8ze:2m+kv *v0f g*al spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table vq28r0 *zb+vku(emhg:fams*?   

  A 280-g wood block is firmljlu dws5w*d1bccn c i7 ch3.j:11+bdx y 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 the7jdjs1b1+1 5c*inucwc: hwd x d 3.clb 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 1-j j0ej1kxv ony03vt a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed atjn-xvok3ej1j1 t 00vy 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 9cs8d6fl +ao e ka oc3h7s,ij9piano to a sixth-story window 1cidl s3 ca7o9 8h9jk,ofse+a66.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must g*-b- mc.v h,nk*oonj9oa l y5be the avera-c9 oj*mo*b5hyakgo,v- nl. nge force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest bt+- zxs5hc5 c c:5lsgto 95km/h in 7.4 s. What is the average power ccxg5lhssbc+ - t5 z5:delivered by the engine?$\approx$    hp

  (a) Show that one Britixuu-n ay*/r 7rgui+u( sh 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 in tu8 bh* cg*va.( *ten+eb+otxoqg my:2he form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to rc 3xw ; idhv h*.2xhrm7l 7*glwzir7+65km/h in about 6.0 s on the level when it is in neutra2ih7lr*g7+rd w7mz wc 3xrl* iv;hhx .l. 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 mou+84yu( vmi 9ec lh)m6yoo/wq tor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from restg j3nr)b jhgf;dm. 8 )bmlx0hx1)n,vi to 14m/s If this motion takes 1.hrib)mv )ghb8 fd.g,xln ;1j mx)jn 305 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of .8b7 -d8asqvlwb*hk k 3.60 m. What output rating (watts) lh-a . dkb8bskw*8 q7vshould the pump motor have?    W

  During a workout, the football players at State U. ran upw9 lyk: ugw.w5f- p4re the stadium stairs in 66 s 9.f 5rlwwe gy:4-ukpw. The stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb armswlwp/kdt-u c va:/ 4)c;r8 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 po: dqi2 jsj;(6s;kxg spwer output of 120 hp. How steep a hill can it climb at a constant s;q2sj(idk psg:;j 6xspeed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dragy7y mse1tm-u) a 310-kg box along a level floor at a speed of 17-t)1m s yuemy.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do/)ctyu,m3 y; h1v/xe8tcxok cwn a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8kp(ngg k4 v+yc9;agta1 m/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If tn19+kc tgg4yap a(;gvhe material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remaiw0g hd nb 0)guj(ub5/veggr.2ning 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 muc()0 gug hb b 2w5jvgru0eg/dn.h 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 famous long jump (Fig. gy gkr+4 r)h53onhb z)6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the43nk)+b5y ro gh)rgzh arc?   m/s

  The block of mass m sliding without friction along tu2(k1f fnglk6 5rrxe:he looped track shown in Fig. 6–39 rk k1:6n(25eugfrx lfis 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 fell 370 m after jumping from an aircraft witrm oz-b0vp:+k hout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate b+v0zm-: pkr o
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed (7 im)ejd: ,plu5po 27 -bxzjzd 7l9bkrFig. 6–47dz9j : lp)pjz72l- ue7xmboidkbr, 53).
(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 cli h9x.) x3q ykxbgo+su2oc :r*bmb is made in yh 2x:+*gqkcsbr.bxx o 3o)9u5.0 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 y7 f6y0z1 3ttcua:xs mcc:) 7jt-(ohcwda y3ta 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 42z. 6u5v( j ij;v6wr1zpgqsyo7,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power nee wpjyjz5 q z62o.1viru(v6s;g ded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fal+oc; v.q1 a.meln2lg wls vertically 81 m before striking the turbine blades. Calculat;+21 neo. qwgl.amc vle
(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 verticbw6x b svu5kiap,5:w )al 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 doesn’t depend on the saux s: kb 65i),wvwp5bize of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into worhc tkm4 xq8m3;wdv18nha)w z,k, how high could an 82-kg man climb a ladder if he wenc;t81m8q ,hz)vd kw3mh4 xawre 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 upwat:fhv 2syj(i8al i.+7uhj7xbrd 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 insid2y4 zs-i n9j;5pwjmikvt-:ll6ktx 8a e the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the sca6s:9 ;vlp-lym4ktxjjz2k -atn5i 8 iwle read at its peak?    N

  A 65-kg student runs at 5m/s graw0 5swvjm23m dbs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his v w2mmd53 jw0svelocity 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 athw5jm /zk v*i a 07zg3g;vlc9hqlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used /5vm vgcwhjqlizz *9g307ak;to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpeky c/s-yb f:xt/ qoxa,:f6u n+d by reversible turbine pumps from a low to a high res6+ykny: -ab ft/uqo,/ sx :fcxervoir. 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 spw7mf;85m ue doring stiffness constant for 8fd5m7weumo ;each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up9 5umyevg v8;t 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 in 3.2 s, how w,)4gkkpe c m6long will it take to accelerate from 55km/h to 75km/h Assumkk) eg m,cw46pe the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), thqy rfsu0ri4 ogyp8 +;9e patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is fr8i0 ; gqrpo4s9uy+ysloping 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-uv7g0xe u6ge 8kg rock vertically upward a distance of 500 m, what was its velocity when it 7 6vux08ugge eleft the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate debeu 3-d/(a b,mjl a0of 95kg/s (a) If this water wheel is set up to provide electricitm 0j/e(-dea3d,b lbu ay output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s