In what ways is the word “work” as p-4us - guyggmf is+ 3qh21c(zused in everyday language the same as that defined in physics? In what ways is it different? Give examples of - 1f2hgg(s u yqcpu+3sizgm4 -both.

Can a centripetal force ever do work on an objeeiaz n98th93g.-lg tycwato+k 88x s 3ct? Explain.

Can the normal force on an object ever do work? 1a(k77c6c*zb rmcm, z7wr zf jExplain.

A woman swimming upstream is not movingba*s(rb(pw,e;l/urc+p- e i m with respect to the shore. Is she doing any work? If she stops swimming and bm,uapw rc/;(bi-p l e+(*rse merely floats, is work done on her?

Is the work done by kineticfzrmx2q n0zm)p;ap8a:8 l+jz friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth outz ): rp2fnap8 80 jmzxlzq+a;m from under them.]

Why is it tiring to push hard against a solid wall even though;9ov9jj o x3zn;ia8zu you are doing no work9iax ojnvj; ;3z 8uoz9?

You have two springs that are identical except that dn5.jopdi0 )i8ky o(e spring l is stiffer than sprin dke.n i 5y0oj)do8p(ig 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on a d7,yk-yk*ts qfrictionless surface (Fig.6-30). T ykykqt,7-* sdhe 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 gravitational potentia6gu; r4.i;dsfh8jm g nl energy change when you jump as hd.m;f g86 gir4un;shjigh as you can?

In Fig. 6–31, water balloons are tossed from t n7x0 p-+f 2gbxec. ehv2ltq,vhe roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impacp b72v vgqn x-e.h, let0f+2cxt? Ignore air resistance.

A pendulum is launched from a p-i;lo.y d8 wq.fw0 l)fyo 1svuoint that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward 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 equilibriumlqoyd) 1 yi;..8 lws-w0ufofv position? Explain.

A coil spring of mass m r ( ih2 +e+*v nmw6fdlmncx(:xuests upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of cond(lm6imncx 2(hxu+wfn:ev*+servation of energy.

A bowling ball is hung6/jhj 6vr/gn j from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the66rv nhj jgj// 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. Why?

What happens to the gravitational potential energy w3vze7q. u, qvt :txlpp(fcemk / /p*o9hen water at the top of a wate (.vo expqp9vqt/k,zpte:/m3u c *f 7lrfall falls to the pool below?

Describe the energy trjpml0a-z +vdlc s2-;v ansformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a 0wz,4 b*kudhbskier starts skiing down a hill, but after a time is brought to rest by stzu0kd*h bbw,4 riking a snowdrift.

A child on a sled (total mass m) starts kjlm0n,h, wb; from rest at the top of a hill of height h and slides down. Does the velo ,;j 0lnhmb,wkcity 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 ste fqnrh+a(49 jjp over a fallen log in their path rather than stepping on top and j4 jf ajhqn(9+rumping down on the other side. Explain.

Two identical arrows, one with twixu ;iyef +,rwe;ksaq)f0 t3r, ce 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 arrow will penetrate how much fari;y ,rse;+xwr 0tqaf3 )u ,ekfther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in tedu0ir/joh+m9 ,k g89)txj mj krms of energy, (a) ignoring friction, and (b) taking friction into account. Explahmgi d8/rxto+ j0), km ju9j9kin why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greahoo,p5h 9 k2sx2. p m-d9yzyrvter than its original height? Exp omy-s9dr9p5h zxyhv2k. ,o 2plain.

Suppose you lift a suitcase from the floor to a table. The work you dx3m7( cjamc y3o 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) (m cc37yaxj3m the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed r7d46vfqi1 i0r4unuw 9uqyb j-ather than the work.

Why is it easier to ca v2:r0ri / gvujvu k9he(4u+rlimb a mountain via a zigzag trail than to climb straight ue 2vra4ghu(ju+0v kr9v:u i /rp?

Recall from Chapter 4, Exampl /aa+dms x i3sk..(wfqe 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fk .s/msixqd 3(.+fwaaig. 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 the gravitational force k u;e /lp:o9rywhen a 265-kg pile driver falls/o ly9rku;e:p 2.80 m?    J

  A 65.0-kg firefighter climbs a flight o)cxed/a/ edh* 3kvwzr+8wau 7 t;1ydof stairs 20.0 m high. How much work is requirkz/1ytdah a8 w;/ 7* dd)we+urev3oxc ed?    J

  A 1300-N crate rests on the floor. How musn9jfu8awpjg 0m4q(gb)6 ;lich work is required to move it at constant speed (a) 4.0 m along the fln6q ;4)jwlf bmggasiu p08(9joor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did thed xh-oz7nm-1 t movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor with d --1mxnhzto7out acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a 7v(s p8b+os yofloor at a rate of for8+(v p7o oybss 7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thicaj; zzuwn 9l-z2 e*iv+k with mass 1.7 kg, lie flat on a table. How much work isuj+iw-ea9v*lzz zn 2; required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might ky2njy 82-pwd,,; *j ulip)dghlx da zu) v4d+not otherwise be ablyu)v )+nlkajd*zjp ;pduw hd4dg2y2i-8,,x le 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 kped3j;r 54 4-zv1s5 jcwfjoujm-n3n bept from accelerating by a man who is pushing back35 zcnb-4u13-j;j jenof 5mpjdv4w rs 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 mass M an b hv3) acccu q2.wm-*lacceleration of 0.10- b)cm.3ac qvcw*ulh2 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 distaburxd k )c)l xsp60*c4;qa yo6nce axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varieoq3ov aca19v+s as shown in Fig. 6–37. Determine the work done by this force to move the object (a)31o +qvcv9aoa from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on 8ie h7ozjr; 65yf,n d90 1h+grqrspck 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 3c )m)m2bf1/, )phphyy tlj tsdq0,q k/3sstz$5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has i1t r2fq x7(uc(1ff2ujh o. hfots speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requjn.qzvg(,ljs6 r- e6k/ )jzw jired 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 travv;w(h* -wbj x htr6vzkh**frl -r*dk 0eling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an acp5mecw+ v.y v2m5f:n ;kis lf9 -)ehnverage force of 110 N on the af5mw)f5melsy:c2v ;knvec. 9nh + -iprrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm wh(;cvns8ql yq/yz-y0 4fek3ko en the ball is caughtv03kyqoly4k ceq ns8;/-(zyf . 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 facg4w src7ry-o 8tor will its minimum braking distance be increased, assuming all else is the sgr4w8c -r 7ysoame? Ignore the driver’s reaction time.

  At an accident scene on a6x7mnvw c;ma zz9 ,+8mwv;m go level road, investigators measure a car’s skid mark to be;6zv,a9m n;m8mmoc + gw w7xvz 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 the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it rg8nns(rwkt1 / eaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if (t1krwgn/ n8 sthe distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if+srwmr1 iu;.9tye5 iza.ccw4 thrown straight up by someone who does 80.0 J of work on it? Neglect air ui5ieys1 . ztw;4 rrccam. 9w+resistance.    m

  A 285-kg load is lifted 22.0 m vertically with khju1sc8/hpw. q5 he y*(nkf6an acceleration by a single cable. Dew k*1( q6hy/ u.c8sfkhjeh5nptermine
(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 st,y. lr-djua l2iffness constant, k, of 440N/m How much must this spring yla,j ul d-r.2be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings fn(vw2p : hph d i1d.q5sr/*bjcrom one branch to another 1.2 m higher. What is the chan qvhn1w/p5h :sidrdjcp(b2 .*ge in potential energy?    J

  By how much does thewrxhpx3m )efa. dp-j39 r*c( s gravitational potential energy of a 64-kg pole vaulter change cad( .xxpps)w9 3fr em -rjh*3if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whe, 5 sxzksg26eqac x2r8n it strik6 r5ksgc2zq xesx2 a8,es a horizontal 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 2.10-kg book f9 fmid5qir56+:t reb hrom the ground so it is 2.20 m above the ground. What is the potential energy of the book rela:i 5bmrefti6 d59r h+qtive 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 elevationh48z4 k s bk-bn5+rgey of 1600 m and climbs to the top of a 3300-m peag4s-khbr by8z 4nke 5+k.
(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 v4b+t,3kguq4s8d x tuaertically next to a ruler. The 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, where will the end of t,d3tus xga 8t4qub+k4he spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speer:zlmv/ i ;p6bd (5.3m/s) and grabs a vine hanging vertical / :ril6;vpzmbly 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 g8igkcv ( 2sh+6*p9awdf.myp 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 given a shove up a frit b86dtj,o wn:c-b+ bvctionless 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 transf (g6 nqpcl +afu05 xcmz2qvs- k(2el*gormed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar wi *u mqx pg 0v((-n2kfcsl5gql6+ez c2ath a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of am7an0p m9 en0b platform with a speed o7bn0mn0pm 9aef 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 consta. o784e r9 ikh,g6 yt 3zwkyuan(rd r/h1m/xlunt is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwar1.yuam4rh6r k k9 tnwy (hr/ex/d7,38g uzlio d 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 l59**hpxd 5xcd hxaxt 53vp8 wh1xz -fcooped track shown in Fig. 6–39. If the block is to rhx515hdhpxp*f dxcx3 awcx85 z- *tv9emain on 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 to the end of a spring (spring stiffn i.xql4kb :3bz:qurd;er q *3t*6ww cfess constant k), Fig. 6–40. The block is given an initial disbw;. tlk fxuw:b:q6 r*ezqc3 *3qir4dplacement $x_0$ 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 whomt p0rbq ei9cywq 9 mj.x7(ya a35g33gse unstretched length is 12 m, and falls a total of 31 m. ( 70cmryba5( gqi 3ypje 9t3. gmw39xaqa) 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 caqsz l 4i8x9ii:r shown in Fig. 6–41 is dragged up to point 1 where it is released from rest.ix:l 9s8i q4zi 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 12 m/s ath x h :*r95xcrd3+ tjgeq0vzz: 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 bottomlc1;qubdv i 53 of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest13u5 c;qildvb . Let M be the total mass of the elevator and passengers.

  A cyclist intends to c)ok.,3,9umo)wq wvkrzya0 imycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 59 cv:+ehfitn zhjmqk qea;.eb ( b7:9 (cxid,kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is pcm f( kqt ci 5ae7 en9i(: h+hxj.z;,b9qv:bderoduced 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 with a sq2rr*8kv k j8tpeed of 2.2m/s How much thermal energy due to friction was gene kv88rrtjq*2k rated in this process?    J

  A ski starts from rest and slides do *k:,q*0f k fpzgv;ac vglv d*5g(cv8dwn 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 gro 6r e9rkywk6 +uwnz:u- 3u*z eebm8fb5und.
(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 bounc. w ml(b+loyy;es back to a height of 1.5 ml l;wb+(o yy.m.
(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 ac:;062wanqnkd q w* /p6nm5e8x w hwmzdross a floor with a constant horizontal force of 350 N. For the first 15 m the flooxakw/ *8qqn 6w65h2 d0 ; pnmezwmdnw:r is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If kum(n+;m*/l6)k cmyzqa o;n rthe average force of friction is equal to one-fifth of its weight, wi*n ;lokrq uma (y6 /cnzkm;+)mth what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12una c-s2v;y2 x wb*(hom/s reaches 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 blockh-4u;u axjp j, 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 before stopping and turning back. What is the coefficient of kinetic frict ujju;,ax4ph-ion between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sprinh 6cry+ 4hb/qng, 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 beyond its equilibriumh qnb6c4yh+/ r position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 07bdg g9nur5ykkt;xd*d* v4t 980 kg including pilot) that was launched horizontally at 500km/h from a ;d rb5 vy79tkktd0x* n4gd*ugheight 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 motmdsog *h 3oeufhu;gn0a4b-/7 0 ya*,bo:it tjor to lift a 315-kg piano to a sixth-story window 16.0 m above?oob */utu4ab :ehy3do naj,*s-0gg ih7f;m t 0    s

  If a car generates 18 hp when traveling at a steady 88km/h wj;srud)a 6 bxk6 )yje*bjhe 2+hat must be the average force exerted on the car due to frictiojjeh*e a ) br)y626j;dukbx+s n and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7 7duzozj 5-ky5.4 s. What is the average powe kzuo5dzj75- yr delivered by the engine?$\approx$    hp

  (a) Show that one British horsepo 2mbn21 ayv bexvzt1m 4lc51(mwer$ \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 of “kilowattkcbfq ,0v lp /t0f,:fu:2 gtkr-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h imnlokanppq5 j /,27w.:un p-dn about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car 5k/ qoum- la7wjn.p:d2,pn p ntraveling at a constant 75km/h.    hp

  How much work can a 3.0- ;- ul7l3aehfvhp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m0epll. r2dhl 6l -h7viyr,n*c/s If this motion takes 1.5 s, whatrl nlli -lv,6. *chey 2dp7hr0 average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water2svfem(ux3 bl-.w 5u d per minute through a height of 3.60 m. What output rating (watts) smd 23vu5l(-e bufws. xhould the pump motor have?    W

  During a workout, the football players at State Ux+px a,)b :cxh. ran up the stadium stairs in 66 s. Tapbh,:+xx x )che 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 cyclistoacd) 9:;xpr:c bf *tn climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill 0fbt9t z:d nm+ sh0;ebcan it climb at a constant speed of 75km/h if tb 0 nzd:9s efht;m+0bthe frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg boxd poaw)nv:t: l7deswlu5b809la9 , rd along a level floort soa:dvu 9 9llre50dwal d,b:w8)7np at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downjcsor2 m3 qm79 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(8km/h) bum ih ;hvcu;,o yxo+jx2oy co2vc++t*p4ezyt ( /pers” that are designed to compress andojo+ ocvy;pcui/ovt 2h+*+4t zec(x;y2y , hx 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 solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the(g0ey xibg3*,yt h e96cde x/6anof-q ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to staefa dc96 e g6nb 3t*oqiyg(x/-h,x y0ert? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 O5yojx xp24n 7awj)cp-. e/d: ul. hf;:vwuwxtlympics 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 t:j 7xdwo/.yau5wc t phn 4xe2. :;xvj-p f)uwlhe top of the arc?   m/s

  The block of mass m sliding without friction along tn7sh1gx)xp 3s he looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very th n7)xs3spxg 1op 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 wbozc1ioq7b :( ithout his parachute opening. He landed in a snowbank, creaocoz:(i1b7 q bting 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 end is fixed (bbg6nlrls6 8 8pj4 te:Fig. 6–43 :l n8 g8letb66j4rbps).
(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 clbz *g j*a4eef-h1 wf:rimb is made in 5.0 h starting at an elegfzhwje1r bf ea*:- 4*vation 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 elevator is 28 m above a huge spring (: jjx sk:ycvl0ey u6u/gg36l)$k=2.2\times10^{5} \mathrm{N/m}$) 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 m4el+ vqg1y1yu ove 47,000 people per hour. If the average livgqy 4uy+1el1ft 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 aay5ulw yb0- -knd falls vertically 81 m before striking the turbine blade-ya-ubwly5 0ks. 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 circrj)3 z;u *h ah,cw)coyular vertical 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 size of the loop or how fast you go throughoh3zc),jhra* ; wu) cy it.    mg

  (a) If the human body could convert a candy bar dir5pmo7 m )q*ndpectly into work, how high could an5o 7)mndppmq* 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward a6nj0;rv 9twapsva4q( yp7 q6 ingle 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 compq /dg5o t(q.7,jfa ihhresses 0.60 mm, and it tells you yaoq/fqh 5 7d,tj.ih(gour weight is 710 N. Now if 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 a las.cq 8y2bvh-b1 m9oc9no1 lkake (Fig. 6–45). He rekl o qybbcnh92 vc19.a -os1m8leases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m(y(9 h ryn;3yyfbu4ix in 9.0 s. What minimum power output was used to accomplb y hrni4xuyyy3(;9( fish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rsd:9 f qog)c6b2 aq4lfeversible turbine pumps frodfo al2c :f9b4 q)sq6gm 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 stiffness con4t9wyl-h/ 5 0 /j9kfrlm jjwfdrj18 snstant k is cut in half. What is the spring stiffness constant for m-tww 9sr8jnyl9 j1dk/ 5rjjf40hf / leach of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 enwx6ewm6v8e vsd8 /:6fp-s y- e3odappyz* -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 55km/h i.0 hgnw840gj,jnfsq7pvv(d in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Asn4ind,pv( v8wg sj.0ghq7jf 0sume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pat6 *n (yoq/( w9ryffbcmient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from (yf (wbcqr6* fm9yno/ 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 500 m,jkkb-7a-dkunv uw 42: what was its velocity when it left the volcan u7dbjv kkuaw:-k-n2 4o? $\approx$    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 -akan/w9dbfyf3k+ r3 l:q: k+fkm 0phm at a rate of 95kg/s (a) If this water wheel is sk f0fr3k k/amn-f k+bd+h:9q:ya3lpwet up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s