In what ways is the word “worhmab1mle 1-; k j-jj4ik” as used in everyday language the same as that defined in physics? In 1a j 1k-j;lh ei4m-mjbwhat ways is it different? Give examples of both.

Can a centripetal force ever do work on an objecc17raf*0:ird0q do6e9alc manzl 01yt? Explain.

Can the normal force on an o d *v9h6jqhbsr 43z8ombject ever do work? Explain.

A woman swimming upstream is not moving with resn gd+/9w )7fj js86r4sqjjfqhpect to the shore. Is she doing any work? If she stops sd+/sfqf)49h7j 8 j rj6ngjqswwimming and merely floats, is work done on her?

Is the work done by kinetic friction forces al cp-q**g rle rth5,g5yways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out f* hrg*e tpqg5r,-cyl5rom under them.]

Why is it tiring to push hard against a solid wall even ,mu*7d.cc .xod cy 3htthough you are doing no woxcdcdm 7 y*c3,t.hu. ork?

You have two springs that are identical except that m1nhu cu c onjeb)0d(p q/x1.6spring l is stiffer than spring 2 mjd1/ n e .6q0u1uhbo(npxc)c$(k_1>k_2).$ 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 hodthc mz c1h.we ;3.z,srizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block mtcs. ;1, .ehhzw3czdstarts 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 potential energy change wzag i2w198ot hhen you jump as hiw zh289tia1 gogh as you can?

In Fig. 6–31, water balloons areklp a,2.2jr 4z d7k/tr 0khojjrj ,+cm tossed from the roof of a building, all with the ,pj. lcrr2o4 kkjktdmj0/j+az 2,rh 7same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point thac+ pr)c/) hfrjt is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an j +crr )fp)ch/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 a mdx jr y5ex3;li i-(2ytable. 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 ;3 5yrjimx-ey ild(x2conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The i8h01ssilitfqe 7oz l 9 ,ze3* )b/quatnstructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the i,9the 8t qbl z1*70liuaof)sz q/es3instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy wh))k d yhejiena9.8ssw*o l y+1t6g yd/en water at the top of a waterfall falls to theg+*k nw))oiyj ehds6 ay1 8l9/.tdy es pool below?

Describe the energy t, /y;yo vkdnw7z ba3,zransformations when a child hops around on a pogo stick.

Describe the energy transp4wrqule)k y (swy8r(m ,1 -iuow.j3 uformations that take place when a skier starts skiing down a hill, but after a time is brought to rest bly kqy)wmou wu48 u1r(si. w-p3j(er ,y striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heigh3 7pb mx(vivq8 83wboit h and slides down. Does the velocity at t bmp8x7b3vivi(q3o w8he 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 steq/.x; t.wa /-u2 qes7lo elqgw rki3k8p over a fallen log in their path rather than stepping on top and jumping down on the other side. Exoxkiwgsq38el.a2 7we u . /lkq -/tr;qplain.

Two identical arrows,s, *lbhh gqw-/ one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the g- lhq*h/wb ,sslower arrow? Explain.

Analyze the motion of a simple swity0:k2j f 3qvjnrb/lq:l9 z6cnging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock hav9nyq6clz jj2bl0t 3q: r/fk :s to be wound up.

When a “superball” is dropped, can it rebound to a height greater thq08 4n57cb qfhcp,x znan its original height? Exp7x f40nc5,cqb hn q8zplain.

Suppose you lift a suitcase fro 6n r5-vkkr4r.,eiyn :yavx g3m 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 alongriv3 vxnran k4 e:5 .,gk6y-ry a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neevo+ppl+rdc .9 cgf*oke8t0d0z ;rsa6ded rather than the work.

Why is it easier to climb a mountain via a zigzag :9w/9kyfzf-fboq4 i e trail than to climb straight uzwb/kfy9:qfo ei f94 -p?

Recall from Chapter 4, Example 4–14, that you ca-qsamdmy; i7p6; fxc+ n use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for qxapds6-fiyc7 ;+ m ;mthis, using energy concepts.

  How much work is done by the gravitational force z1f:covk, fr8 j2e 3qwwhen a 265-kg pile driver falls 2.r vk 1ze,cfqo2j8 f3:w80 m?    J

  A 65.0-kg firefighter climbnuf)3opuw 02mnh 0it3 s a flight of stairs 20.0 m high. How much work is retf3ui 2h 0nmuwpo3)n0quired?    J

  A 1300-N crate rests on the floor. How much work is required to move it a q8r 92 ahs-5ub ckabf+kg,p6h.fh3ntt7eqi0t constant speed (a) 4.0 m along the pqs8kc ahr3bbf7-5akfei. tnu, +092qt h 6ghfloor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizor5,9c4 g snxlkntally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficie9s cnk,lg4x5r nt of friction was 0.50?    J

  A box of mass 5.0 kg is accher;esne7n eyxxz2 :ae,k; 20w fm827pus+ yrelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the box.sxe spam;wey2,0key rhzf7;72r2nx e 8+: une   J

  Eight books, each 4.3 cm thick with mass +p2nbd2od*r 1 g8smvz1.7 kg, lie flat on a table. How much work is required to stack them one* +pzdvd28sg 1mo nr2b on top of another?    J

A lever such as that shown in Fiqr5o2 rp u*1scg. 6-35 can be used to liff objects we might not otherwise be able to liff. Show th uoqcr25r1*spat 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 isa /im ua8eqzcmqu yo80r .9/.o kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic fo.a ./ oim9 zca0yue/ qm88rquriction 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 di- gnb7j ,k;m2j 4)t7gmkkcban acceleration of 0.27dibm-njb,t4g; jk mgkc7 k)10 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 distance axis is linear and i+id24 6tfj 8lnh(1lm30aijozb8oar 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, r:y-tlf yo1j. varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m y t y1of-j:r.l 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 onmihepxye : 1;hq,ih * :w)ez;v 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,zdj232zj-5ca mlhax jln -;p0 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 facb zw;c48h+*x e ecj8iotor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an mcy42 ktid- 7-3vvsnp7vtc 3oelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-k fr* zhhue0 mz/8-kofr*q1ff .gcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strssof/g5 n (slo0/*arbing exerts an average force of 110 N on the arrow over abs/o/ gs*0r5ao (sl fn 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 (ssl3w.jg +vbn1a eg,glove backward 25 cm whenjeb+sg31l( n s. ,gwav the 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 what factor will its minimum braui lvr(: 2 nkr ;;atc.7dvyjg4king distance be increased, assuming all else is thad.nc7gt:rkul;yi2 4vr ( vj; e same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a clag j g*cn,+.f 6z4t5u queia5ar’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 eg *nzu.c6fq,5aujtl+i 5ag4 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 thykl2 b4c)dpq; e time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the avebp4ky;l )2dqcrage 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 someone w8lhyz-d*1cx who does 80.0 J of work on it? Ndh lx*z8y1w- ceglect air resistance.    m

  A 285-kg load is lifted 22.0 m verr ds;g3*u/e1m *i tvoho+r zy(tically with an acceleration by a single cable. Dem3 ;r/v(h1sdzi*gutoo +yre*termine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this suf-r7 iy8 +ja7; pvk 4asc4l;aw0vkmkpring be stretched to store 25 J of potenai fm; l a4-7aj7vu+;k0ykr 4cpws8kv tial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m8g* dp2lo:e5h+pze hm higher. What is the change 2p5lhmgo+ h*8zp:e dein potential energy?    J

  By how much does the gravitational potential energexn 6y*j elk16y of a 64-kg pole vaulter change if his center of massejl nk*616xy e rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface hasuun7g*qu y0q:k.,ve q speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance o keg,qqu:. u*qn7 vy0uf 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 2.20 m ab2:kdcp +shc b4xb k0r-ove the ground. Whachxkbd 4 -bk:+pcrs02t is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to thjlsl5pb8za ey 966, a2ep) bxm7j(qhge top of a 3300-m peak.alsge9 y2ajxbe6 l8,(zj6 q5m7hpb)p
(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 ruom x(k(sak;d) ler. 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 the spma)skx(d(; koring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vimi8w ygz ei4*3:f:g g7i-i :ago a7hlsne hanging vertically from a tall tree in the jungle. How high can s 8:*fiyeli 7 z-ghiogmia43s:awgg7: he swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionsx9 iw:y/q q8k;m fx2yless 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 ,k ze1, cdboyl u*y:a1+v0ym za frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational potertjgy5oup*lj95:ln7 ntial 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 l 9o5jyrg*5uljtp:7n .7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwar5+vo kil .y cyw*-jncfb j7j8(d from the top of a platform with a speed .co*nlcfy+7y8jij b 5j (kw-v 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 sphp4 xos.fk 9: hrh/v2bring stiffness constant is 950N/m is attached to a table and isxv h 29f:.hpbo/r4ksh 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 along9(s.cuda z23so y w3ymx2ml(s the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h muszycsx3o (m3 d l(s.wsu2m2y9 at it be released?    r

A block of mass m is attached to the end of a spring (spring stiffntzu c;i3wa evz 61p 3pggc71.fess constant k), Fig. 6–40. The block i3vuzcgeat ;g1 3pf 6w i7z1pc.s given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whos 6g+()zal9luf (iqfase unstretched length is 12 m, and falls a total of+la(qa 9 s6(uzgi l)ff 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown 5)9.s oo,hvp;eujq zo cm-d3k in Fig. 6–41 is dragged up to point 1 where it is rjdp vm,-q5oo)ce;uh9o.sk3z eleased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is th */; w(w zbbmpy3c qhp)t5cmrx*x2e n4rown with a speed of 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 afop4bx5 /+cilw c1:cr egr m75 spring to be placed at the bottom 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 af :li+wco1xp5 4gcb c /er5m7rcceleration 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 u-1ce f3b cq w.m3g.fwx7-kvcwsrfd;;p 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 8ilqvgo *.i x/of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produceo gi8* vq/.lixd in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the botpw0/ 8hix kl5ttom with a speed of 2.2m/s How much thermal energy due to friction was generat0ih xkpw/l 5t8ed in this process?    J

  A ski starts from rest4ncqpvc8 gw2nj/i z-9 and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is droppx7 3kb;-pn4ga ff549pfb qs+7skykwced 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 2.0 m,6z+i4fk edvztj4t *g812bricqnp-k/ and it bounces back to a height of 1.5 mzikr tj p-n 84i 41f+6evzktq*db2c/g .
(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 fro zegf )sp(08duuuc2k:m rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor ie8us:f(z20 k )cduu gps 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 coasvt uvrb:5 mymdub47zv+ c6*r26u b-a 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? Thu4m+ dz vbr:b-62vsv 5tbu*yc67 rmuae distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a ste8l a:n5mizr6p ox42al ady 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 u 2tyeel;:m*c,aq3q b 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 el2c q,u;te*y3bm:q acoefficient of kinetic friction between the block and the table?   

  A 280-g wood block is ficf9l- .g)w 2h9r2h u.whdhiktrmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coeffic- t.9hkh .hf22 whdilg)wur9cient 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 equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (massw sd7s37.0imonc/ q ru of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistanceo./7c7rquwsmds i n03 ?$\approx$    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 j:pg o .uce6ax47xc2o/3jor p lift a 315-kg piano to a sixth-story windoj6c 4u/ px cpgx.a7:oroejo23w 16.0 m above?    s

  If a car generates 18 hp when traveling at a styd1lg,mk rni90x9m8p eady 88km/h what must be the average force exerted on the car due to friction and air relxp80,ng19im r9mky dsistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s1/y e n)j.swqmuvb8ul m/zp.ac. vv)/ . What is the average power deli/n zq..wb1)u8v lv/em savyc p/.)ujmvered by the engine?$\approx$    hp

  (a) Show that one British hor -ngmwjxz(8wae c328l sepower$ \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 “kilowa8v ihkfpd t 1v+zvohvm d:/t..*lx9 xykf9e+ 5tt-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 slowuf b2/--sfb nvr(4 vpwork:7t s down from to 65km/h in about 6.0 s on the level when it iso fv-rb2-ktf(4wn /7urvb : ps in 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 motor do in 1.0 h? 4zwaa)h bgwq09 z26w+q8lkqb $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this m38d5bu p6 plhrotion takes 1.5 puprlh 53b8d6s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water 9 cwga-2wl/8 d, b0 wv9 0o(e ixhvf8evc6orqjper minute through a height of 3.60 m. What out92c9bivo j 0c,80a/o x-d rw(whgfv6vl8 we eqput rating (watts) should the pump motor have?    W

  During a workout, the football playzn+;3cj)fzym5 iw/( gxr mlf/ers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 32 cg/) xfnzr+;wf/5lzim j( 3my $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a + r+ rbr36gh1hysj:ec 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 maximumcy w.m9m+c( bu power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N? b+ m.c(wc9yum   $^{\circ} $

  What minimum horsepower must a motor have to be able to drag agp co3 1k8wh 6mv*tm2hsutc,3 310-kg box along a level floor at a speed of 1.2m/s if the coefficient ofhohm 2tc3,p6t*umc 8s1gv3 kw friction is 0.45?    hp

  A bicyclist coasts down a 7.0 zzliq*vz rs3 /a an o2mq.3+a69ifp u1$^{\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) bumpern,euki7 8z4cgs” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid g7nu,cikze 84 wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offe)sbi4tr4 (sz the 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 an4rz e(sts 4)ib average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympixm) ot 9zy9c(ecs shows that his center of mass rose 1.1 m from launc)ox99e tm cy(zh point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track f;qaobey b + p/w;;5w6iez8od shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the 86/ debf;wo5 awy;;+i oqezpb 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 6kf ih 93;bi0o98sd zp.hxx rsfrom an aircraft without 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 ho3i.bx690 fd zr9s ikxh8h;psis 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,)ycz *m f9zhh other end is fixed (Figyzmc fzh ,)*9h. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the toy d*0 vl*x)jjip of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calcu0*yjj d )x*livlate
(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 9n2i j-6mlqq+w;vd n( v20-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 kb8k0(xiz: vxnjo)h6w8*o*ehhh(y l California claims that its lifts can move 47,000 people per hour. If the average lift8h* o(( 8j6):kxblho n0x yhzwiehvk* 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 69n4)oe exa*fgl (f 7a;9qmygo :+vd yq50kg/s and falls vertically 81 m before striking the turbine bladesnm(aq7;o+ o49yd*gfxvf9)a eyl: q eg . 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 vero:3i3,ocl .cfm em 2kltical 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 i ccom2f3:,lo k lm.3espeed 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;b 4apcagz:b*0p t/fgzed5y pv 249 dk could convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (p 4zf;24d/y:tc 9ae kg*b 5zadb0vppg=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45.0er )*y+-n umuh5:uksla /:xi ah enr0($^{\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 compresses 0.k / dkizb:7byrz6s)tom20 8ci60 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 doesiokc6 m7rdby/i: ) kb z8t20zs the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, u 68enjy8 s1xlr:i6lyop 5e: jand swings out over a lake (Fig. 6–45). He releases the rope8 exn:py elr15:o6y8 ijuj6sl 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 az)6z 2lg.o f t3 7,olwcegiin(thlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was usedli te7z l2oci(no3,gg )6z.wf to accomplish this feat?    W

  Some electric-power companies use water to stsg;w6k;e.bqbe)() 7e y kxstqore energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the ener ;)btqkx(.qes 7wges;6b)ye kgy 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. Whac0xz-oylmcw( d;( wq6t is the spring stiffness constant for each o0w-z y o6l cqwm(;xd(cf the two resulting springs?   k

  A 6.0-kg block is pushed ( fq w)hi(5rix b4y0js8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.27 t(ne7jtao5tnvlo0 q,4y,+ose6 k u b s, how long will it oes+5(e n7064tlabvj 7o,,uoqt ktnytake to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (y w4hi6q )+pnblp6s g 4epi4(rthe “stress test”), the patient walks on an inclined treadmill (Fig. 6–qn64ipe y( +irsg4p4hw) lp6b46). 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-kgyu rwgu5 3; i65rrva5m rock vertically upward a distance of 500 m, what was its velocity when it left the volca w3ru5m ai6g5 vurr5;yno? $\approx$    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 o/2/0;vmreg n7vqwjf05d pyh p f 95kg/s (a) If this water wheel is set up to provide electricity output, 00pfdmgh2vyrnp ;jv7/e/wq5 what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s