In what ways is the word “work” as used in everyday language the same avzh dsep s-ckm8.8;8 ns that defined in physics? In what whms8k8;p.z8-v e d ncsays is it different? Give examples of both.

Can a centripetal force ever do work on a-b :aysws e*8yn object? Explain.

Can the normal force on an object ever do workf0y-yx5 es ;*j,uc eya? Explain.

A woman swimming upstream is not mo9t wc4kp x)6ao.s d25fe k2lgdving with respect to the shore. Is she doing any work? If she stops swimming and merely f9ka6d.f sotx 2c)w2d 54kpl geloats, is work done on her?

Is the work done by kinozi/y* 4s+suaetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a s4+za/*io ysu tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doingra;c0nm+ eae 9 no ;+me0a rc e9nawork?

You have two springs that are identical except that spring l is stiffer t a1 ve5v0b5lujc 46c*id usmo.han spr u.6jul dme*0 oivsv1c c5b4a5ing 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)cta9 x pnxhc 6(p/11b/gusqx on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time ip/t9g/nasq6bupx ()x x11h cct 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 gravitalegoer/) sdvv(50/jfaeh(f f5pyy4 3 tional potential energy change when you jump as high as j5 ae(fyeh(vyrs/fo4 d ev3lp/ g)05f you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildingun d tk14+w,cx+z+l 7g6 zchcc, all with the same speed but with different launch anglcd xtz ulc hzn,+64 cc++k71wges. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above c 3cfiv--b wqq 4ckb.cew/(:l its lowest point in two differee(wcwf-b .3c /4q:b -iqckcvlnt 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 equilibrium position? Explain.

A coil spring of mass m rests upright on ifv9,b,-epig9czfdqtc)d4mwe;1 i : 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 conservati)fc 9i-v;: e9fc,1p4qwb,d eig imd tzon of energy.

A bowling ball is hung fre7dd2* d1c sjw-6p hqaom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stand7dhj-d2s1w*dc 6p eqa s 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 when water at the top of a ww;koz1l p:g o/ate gkp1z:oo/ ;lwrfall falls to the pool below?

Describe the energy transformations when e;tuimbu/ kg h -q n/v5y80j9ca child hops around on a pogo stick.

Describe the energy transformations th6z.yp7yukizsyyg ;; 4at take place when a skier starts skiing down a hill, but after a time is brought to rest by strygz. syyp7z;4 ; ki6uyiking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill ecrsdkmc 0t )ik6(q9 ac (,k2kof height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, k2,(ecqkkism(9 0dc tk)ar6c and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather tha hv.3fqdwv*px( x3r3npm4 a 3qn stepping on top and jumping down xw pr n f.a*qp3x(3dmv3vh4q3 on the other side. Explain.

Two identical arrows, o:8y1z 9s.t 5ej qofmnwne with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a.nz8wme fo:y1 stq 95j constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in t t ogx;ful (si(b16v(terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.v1 6sobx il(((f;ut gt

When a “superball” is dropped, can it rebound to a height greater thajedykbb*t l2kvs zp7v f3)8 :5n its original 8 l5vfykse:)bkz7t2dv3pbj* height? Explain.

Suppose you lift a s,n):likjx5k+uy ee+muitcase from the floor to a table. 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, anduey)+ ,je nmk 5lx:k+i (d) the weight of the suitcase?

Repeat Question 22 for the po2r/;oi l:ulhnwer needed rather than the work.

Why is it easier to climb a mountain via a zi4xl+s-fb1alq: etks0gzag trail than to climb straight ue4l: q1- t0b afkxs+slp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to d9e3dt )x wdua2ecrease the force2 a3d w9xtud)e needed to raise a heavy load (see Fig. 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 5fo9.a qekn 8aj98 wb4jibs-r gravitational force when a 265-kg pile driver falls 2.80 jen k8ao9 i. q4fw9 ab85-bsrjm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.-t. /yzp0d+vthhkdc-v ) s3cv0 m high. How much work is required? v0 c thhz./+pd-vk 3ys-vd)ct   J

  A 1300-N crate rests on the floor. How much work is required to move it xi 3erj00 ; 4mggvyk3+bbcz6e 7sph5k at constant speed (a) 4.0 m along the floor against a friction forcc7x zgi kek5pegs0 6;mybr+3b0vh34 je of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg+re5ot 8/1k+h;zh2 e* qzn 5kn gzchxl crate 10.3 m across a rough floor without acceleration, if the effective coeffi1+ghrn /;e2 l hhz +qek8o*ct5zk 5xzncient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate o:es .b7r aphg fug,1u7f for 7.0 s. Find t.:p,7h bfau se1 7rgughe net work done on the box.   J

  Eight books, each 4.3 cm ruv ser,(2ac 3kg6f d1thick with mass 1.7 kg, lie flat on a table. How much work is required t2 ,dvu61k (fag sercr3o 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 miy xz5hpl8j a 9eck2)4vght not otherwise be able to liff. Show that the ratio of output force, 9y p aej5x 4z8l)vhc2k$F_{\mathrm{O}}$, 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 accelerating by2 anha)4fh) kz5r.qdq a man who is pushing ba25 qh.)qf4ndaahzr) kck 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 acceler15 d*t pgtd,itation of 0.10 g tid, tg*d51t pupward.    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 lioqhm- 47 ,sjannear 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, actwv1j+ho p02xc 5kj2jyp qj n/,ing along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m tq v5nh0joc /+2wp 1jxj,k2yjpo x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle actsypyv+44 qt,e h 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 maq;*c x7k w,jxg9+0ohwscf0m yie:;n css 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 has its spyk9adt6y70a rg t4+zhc1 s y1yeed 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 *fikyk3p zh vyfwdg +3*:i1 qe*:pr)helectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kgcd kb6wb4q;wh5ar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 cy;9zm9pj6y e yc9i :s/ ji.hrN on t jczepc imsy . i9y6j;9r/y9:hhe arrow 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 ,vvqo.ktxx * :uk8h2gf9a 9jx25 cm when *t9xa:xfgk,h9x ko u jq2.v v8the ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by/at7hxcsy++-vgu*k p xco s16 x,5vcg what factor will its minimum braking disuv5xt,pv+y/ s*k ah7c gs+gc6xc - o1xtance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measu q5 (i/kdfule1re 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 5 /iu1kfqed(lcar 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;0obdjrel k6; time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the disl6 od0er;;j kbtance 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 does 80hz7 m yecaswdbmfu8*h*3() 7y .0 J of work on it? Neglect ai8y3(*wzhy* )fusdbmc7em 7 ahr resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singlu7qd k /c gj.0ilqdg g,. b*jx5lui6y6e cab,g5g.g u6ciuxi7l j.bjl*y0dkdq/ 6q le. 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 spring stiffness constantsja5s49 y/qkt , k, of 440N/m How much must this spring be stretched to store 25 J4ytsa j5 9sqk/ of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the5q g2 t4ayh v5yjag;8shu;*qe changeh5tvj4gga 5ye;y q*8;a2u qhs in potential energy?    J

  By how much does the gravitationah6hq*8yv+ ixs oz91gn; k7kkil potential energy of a 64-kg pole vaulter change if his ;6 *yo 8ikg nx +ks1ihz9kqvh7center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal gz24 bzy4br2lsurface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distabr4zyzg2bl42 nce of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is k.fbtp1*oy 0adwg 8j +w9jo a*vod6i 62.20 m above the ground. What i **iod6at +gyw. 6od80ka1ofvbjwpj9s 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 jmw ;pa,uii f r1w/ho+bdj n4nd6429pm and climbs to the top of a 3300-m peak. i19;p+pn ,4jm hj4nod 6 uw/ rfwbia2d
(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 thedm:q9 0p e ls))usn6hi 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 wie :) 9indh0 lssu)pmq6ll the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan -e-qs g,y67doj2cb*) clsxji, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can sd-xbslq6jsjy* i- c)gc, o7 2ehe swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides downdg*4vc4qhs )vmz 0j 6h;how4n 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 frictionless 28z * bflj+:+:tg:2 ztw7gu*kgq.zakjdx*mwg ) .0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravequusva5 -c8(6;fkgg o1eo (titational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/sgsuc -6oe8k51 g(;ovq( efa tu.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a pl rom fk1 9uzjc:e8-t+3xs1 *y typck)hatform wit zo-c3ytcu1s fxyk+j8mp )9k 1r:t h*eh a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose springff05r n. c6)lqggr:po stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-k.clffr gr po0:g5q)6ng ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown ix-- t)jkh:m vvn Fig. 6–39. If the block is to remain on the track, even hvtx:jkmv)- - 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 stiffnesdx+ .asr5bx 8jny5,ae s constant k), Fig. 6–40. The block is given an inix5 ,xres y+nbdj8.5aa tial 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 tied to a bungee cord wd 8ga6qqn* i/whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, ass *6niagd/8 qwquming 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 dragct/wvt+ l ;8dcged up to point 1 where it is released from rest. Assuming no friction, calcu ;wcdt+l8 tc/vlate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of-y i8j3 g-qdpk 12 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 ofwqe2sw( k/+b+ kovmz3 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 brok/voz2e+ +ks3qb(m wwught to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to wc0 jvp4( u-+- 8h/xfcobtaec cycle 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 kg and traveling 95km/h in opposite direxp:9tvd1( skteti;m9d(3m; qo *bb kzctions, collide head-on and come to rest. How much thermal energy iso1dst*kke9tm;;vdq9(t : 3mzxp (bb i produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m r 2j)+qw6y nlhanbiz1i q1/hy) imidr8a;4) uhigh and reaches the bottom with a speed of 2.2m/s How much thermal elrhd z b i+y18y)i)qa1naqu6w/)2 i;m4ihn j rnergy due to friction was generated in this process?    J

  A ski starts from rest and sly3( 22qs1edusxd wa cwm:-ic;ides 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 froa wm /ih3 5yvq6i78,kg)dqoarm 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;c+ . qmun0dfq a height of 2.0 m, and it bounces back to a height of 1.5 m..fmn qq+u;cd0
(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 constant hor8g/1r h) iyb69h ehimzf v75rcizontal force of 350 hibh r cizgfe9 7/1m5yh6v) 8rN. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poinh5pvl i 0unq9v3.x:c ztnel;1 t 1 with a speed of If the avex 9t0hiv5 l qlc nznvepu31.:;rage 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 steaak h -gddw. bzs+25;hds w1fi9dy 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 li/w .and2e),d si7 vc,wq-sh h-ag9 ujeght horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the- sqjehnaw9de h)d i7sw,v.2 -g ua,c/ 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 x8s/8wtjj zk lt950gn-b +zpr 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 thxt 9-zs wkjrp8gjb0 zt+l85n /e 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 980 kg includi ag+p,mfc( rfz)/dmbp4xhrbk z )25+fng pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a sperbb45dc+p, g(rf/mhf ) p)kf 2zzxa+med of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-storyy7sjz6bf jn4v u;+q7r window rsbjyuf 7j v;z76n+q4 16.0 m above?    s

  If a car generates 1a 0r4t7)hd; styutg k28 hp when traveling at a steady 88km/h what must be the average force exerted on the car due to frictuhtsrtyt 2kdga; 074)ion and air resistance?    N

  A 1400-kg sports car accelerwyt(v8dh:gix ;7m o)fates from rest to 95km/h in 7.4 s. What is the average powerw7 mdvo(xiy8fgth:;) delivered by the engine?$\approx$    hp

  (a) Show that one British horsspftn8cf k2/e;v+xn (5.oabn;1 nf chepower$ \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 ex; yipg 3ci7u;xpressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that heug0 o/2),gjnzhoo4 os r 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in /g o,0o2o sjnzu4g)ho neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mvtpp 7-p) 9at3w tlxcmi+ hdvvm5d1 8*otor do 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 moxm+mh/t 4nw/o6v is8 ftion takes 1.5 s, what average power was developed?mhv m4xst8wo f/6+n/ i$\approx$    W

  A pump is to lift 18.0 kg of water pe5; vgu( j xy)(*dso qne/v/mqwr minute through a height of 3.60 m. What output rating (watts) should the pqe)om sx(/ gq 5d/u *njw;v(yvump motor have?    W

  During a workout, the football players at State U. ran up the/w-p7 pqfqgy ( stadium stairs in y/p7gpqfw( -q66 s. 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.th,m ,rxu f1z9sk:dd1i upn ; 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. Hor+-en5u uofb 6w steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N?r5e+-bufon u6    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg b*awv+ gfa-6 zlox along a level floor at a speed of 1.2m/s if the coeffz-f6lga*w +v aicient of friction is 0.45?    hp

  A bicyclist coasts down a 7 a; l:u:*vedud.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 by -vz7ebtdf/615irh4 msm g7 built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper 75bv17 m tif /ebd-gy4z6 rshmbe, 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, 3v/bzyj3e0x d:-azfm at , k6wand 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 la3av 3bmet d 6wa0z,/fzy-j:x kying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympicglu0q0h mv5fg:ymf +6s 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 tra6mfmug :fh q+ ly500gvveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown kb(ws*h )dm;cli1x) o in Fig. 6–39 is to remain on the track at all times, even at the woks)c*lm; h(x) db1i 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 without his parachut(nnvghtm7. s7c,in67 rj z;pne 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 ter7;6nms vcp( ,. hz77injgnt nrminal 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 ig. +eomny/tn( l5 q*ht +*wr5nvs,w ojs fixed (Fig. 6–4jthyw+n, oe*ng 5/*s +omrtv nl.5( qw3).
(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 cl0-s7/xn;cg d4kup 99ly s h);rrzyfdvimb is made in 5.y9vsn0 -;gh ;7)z fd9k r4rxsylpuc/d0 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 a 920-kg elevator is 28 m above a hu l txq-q8m7uu0ge 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 47,000zxlxnk) bxq0cegyf p+nwrn39 u/m; 4) ) ml0j- people per hour. If the average lift carries people about 200 m (verj)f;rp9mel/ nc z)34+myx -k x)nb w0g0qxlnutically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before fsat1e i+ql 5mvx-x5/strev/am5f+1qx5 -ix lst iking the 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 verrmlxra/yt+p66 x 8;h mtical 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 8htx/6ma xpr6yr l +m;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 through it.    mg

  (a) If the human body cg19;yca;*b4vg jg mzh ould convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he werea;4y*91 gcj zgm bhgv; 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 ans(pz 6t sz9:i*jxikx)3we,j ggle 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 ma coerlva9f 36(4h3b inside 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 l693 rhvm4 3bca(ae ofscale read at its peak?    N

  A 65-kg student runs at 5m/s grabs ays)k:3a6u9carj.bkf-sxe p 846a ov; .ac wav rope, and swings out over a lake (Fig. 6–45). He releases the rope w 96waoa46c3yxv; kb ef -8vascsk.arp .uj) :ahen 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 climoa 0dyp zf h,iy+3+bg5bs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish thiyz 0 o ida3gh,p++5byfs feat?    W

  Some electric-power companies use9i ghb/w 6s2hrn 5h-hq water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservnbh6gih 2sh/9 wq h5r-oir. 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 78q n: hfksd9sconstant k is cut in half. What is the spring stiffness constant for each of the two kq n897ss :fdhresulting springs?   k

  A 6.0-kg block is pushezyemy. 3wxv+nzq ))es :j+x(o , r(ekwd 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 35kmgd 8w15vekgq(9rk n*e/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictiona(v9k5e ned8gk *w1gq rl losses.    s

  In a common test for cardiac function (the “stress test”), cwxmu7e9t7(vthe patient walks on an inclined treadmill (Fig. 6–467w(utem 79cvx). 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 v 0h ctct/ o3ae9rj :ye0vl ra.5l9a.qrertically upward a distance of 500 m, what was its velocity when it left the volcana5j t9al ac03rr y tv0/hoe.q el:r9.co? $\approx$    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 heigf66; 12dquds64jfwh 4uxh k skht of 2.0 m at a rate of 95kg/s (a) If this water wheel is set uqh4sxdsw; d k4f6u uf66hjk12 p 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