In what ways is the word “work” as use-qo(:-mx-sme 5x xsted in everyday language the same as that defined in physics? In what ways is it different? Give exampltxm5e-- mq(e :so -xsxes of both.

Can a centripetal fogmc.a o1koc4soseg) e,c+. ))tm7 hxc rce ever do work on an object? Explain.

Can the normal force on an z l(qzv4z (yn2hiq( 8d,mnol6 object ever do work? Explain.

A woman swimming upstream is not moving wij ,4exm1e osz/yr( hf4th respect to the shore. Is she doing any work? If she stops sxo /se,4fj (h1m4y erzwimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [ pvn 19ijk;2lgHint: Consider what happens to the dishes when you pull a tablecloth out ljp9ivng 1 2k;from under them.]

Why is it tiring to push hard against a sol fme+a*mq:4r)jcwc6 k, es)bxid wall even though you are doing no wo bk)e4f, jxa s+w)r:cm6qemc*rk?

You have two springs nig jq83a7b;p3u uj 8is5ja1tthat are identical except that spring l is stiffer than sprin;u8p7aitu3a jj3n 5s8qbi1 g jg 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 ap: w2+n kdgjo* u,hro1j:/u gk friction:dg/uk: opor1wug jn* +j hk2,less surface (Fig.6-30). The 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 potential energy change when 7 5r3v exqr+)ivxrng(you jump as high as you can?v (e7r3 vrqxg n)ri5+x

In Fig. 6–31, water balloons are tossed frp 9/h h1hn(ewvom the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air rhw/ ph 9ehn1(vesistance.

A pendulum is launched from a point that is a height h above its j4e0 d)kw dti:9436kgi b ryvjlowest 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 direcj ejrik9w46 t0:)iyg k4dv3bdted 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 table. If you compress t6b,2 rfmhrqn. he spring by pressing dohb.q r6 2rmfn,wn with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the k6c cp f4 28v1t82hrmhdpf u7cceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall wc fv8cch4mu7hpd26t pf8k r 21ith the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the grpx(2/( cy0vrrxf,pq favitational potential energy when water at the top of a waterfall falls to t2q c(p fx,(vrfyrpx/0he pool below?

Describe the energy transformations when a child hops around ont+:wyuzki( tp/4q t7c a pogo stick.

Describe the energy transformations that take plxdfz9 j0 ;4 5fv6l2bx)rn o -td4garrqace when a skier starts skiing down a hill, but after a time is brought to rest a4rfrbt jo 4n29)vx6x d0 -dlqzr;5gfby striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of 2 ynrg)hrh*:ca hill of height h and slides down. Does the velocity ag h)rcy r*n:h2t the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen lo28(l0s 5fjyi :ikb9mth0j zs5 almyipa x+3k+g in their path rather than stepping on top and ju y 0 x5ymha++s9mtbja2l5ljiz3:pik0 k f8 is(mping down on the other side. Explain.

Two identical arrows, one with twigpawbz1;, 0ys)r*gqj ce the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the a,;bs*jqarg1g w)pzy0 rrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendul6b;nx0qlsk3(x: wbp qum in terms of energy, (a) ignoring frictiowkp6bxx: q0nl; (3sbq n, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than i c lfb+*;v.llots original bl+fv c;o.l *lheight? Explain.

Suppose you lift a suitcase2)rr+th nv9jp 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 pathrt +n2)jphr v9, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for mf* .dajkte-3e5jr0 d the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than e,o16p6lfu;l9- lbht k c0wechd5h3 z to climb straight up?o6 hph khdu5, 3lclc-e6fe9w1 z lt0;b

Recall from Chapter 4, Example 4–14, thatv-equ1 x6b rap6ix7qaag:a1 1 you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–3-x7: 6eapruab1qgqvix1aa 61 4). 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 g1+b df 8+cifzbravitational force when a 265-kg pile driver falls +ffb iz+d81 cb2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is p u,3*t;im bgxr3lnpbz84 b 1crequiredrm3bt b l pi z4x8pcn;u,*31gb?    J

  A 1300-N crate rests on the floor. How much workl .wnh 9gid-+v is required to move it at constant spev .l+hig-wdn 9ed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1gdwc:ctz 97rq+lv- i)0.3 m across a rough floor without acceleration, if the effective coeffic9qi-ct+)lvdc zwg : 7rient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fl-ok.dv47tfn euu q3x6 a(it7koor at a rate of for 7.0 s. Find the net work done on the box3e7-4 6kniko.( d7uxfa tqutv .   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on ao yxl;( du lg;nu;1f 6micp*/o table. How much work is required to stack thel(;*g; yilofup1/o xu ;d n6mcm one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff omvvv/x;l b 4pn3b dkp7o63a; objects we might not otherwise be able to liff. Show that the rat67 a/b3xk4bmnvp;voo; dv3l p io of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelerating by n,*roqjlf n bgyo;iy6g(0:x d3 mh)*ja man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefo*b; gy(:n jl*od3mhg 0jnq6rfxi),y ficient 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 accelei*d5ec5m.t hdc /g9ue . ndidp,4xr-tration of 0.10 g upward. u9 / tmp.nti4 cx. g e*55ddiedrd-,ch   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 tsg4; mrt7f7 mghat $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies ast;ob5g- hs )u1gz,ry s2h.1huvq7ux s shown in Fig. 6–37. Determine the work done by this force to mohz osbu5 tushgqrx)y h1.s21 7,-;v guve the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerte9qj0kh+ uf 7izvtx;v5d on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass ofyb 5yff, +ylt9hs0i,j $5.31\times10^{-26}$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 h w/;w0zltump;as 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 electrn gm4czbm6eq2( r ksp m9mu)w 1hi0/-won $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 travel*xo9c;h; ivawdjc9 5 6vw;hxeun:) g king 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 fxjp c2ihq.x3ylcz 8 d0(d+nmxb-fy )/orce of 110 N on the arrow over a distance of 78 cm.f8+ ddnzx- j0l2 b.xhy px/i )m3cycq( 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 o,ze g8fzt .t1 ,wbl/d25 cm when the ball is caught. What was the average force exerted by the balll ,z,gftt8bdz o/.e1w on the glove?    N

If the speed of a car is increased by 50%, by what factor will ertt nd pp i1gw9(d:+,its minimum braking distance be increased, assuming all else is the same? Ignore the drivdrndei+ 1:p wtt,gp( 9er’s reaction time.

  At an accident scene on a level road, investigators measure a (-h4 iy xw0wyjcar’s skid mark to be 88 m long. The accident occurred on a rainy d4 yhww(ji0 -yxay, 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 reaches tgvl-d n80 s.jche plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air res n-lvj0sgd8c.istance 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 byv);h8xgu :kzs someone who does 80.0 J of work on it? Neglect aiv z gh;uk:)8sxr resistance.    m

  A 285-kg load is liften :bv18a fnk 4g5+ztqkd 22.0 m vertically with an acceleration by a single cable. Detv5fz8tn1 :k kbnaqg+ 4ermine
(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 (+iet az ,k1a cuzp:tizkpw. /3w0 qk(stiffness constant, k, of 440N/m How much must this spring be stretched to store(ita/aw.t :kz0e u pz3+zkip,q( ck1 w 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What iaywynj8pg ko1/(-cl 5j(h 1vi s the change in potential energy?l1g(n-j1c ay5(jo8v/wyh ik p    J

  By how much does the gravitational potential energye*nrsgo;1wy7n;almp ./*bss of a 64-kg pole vaulter change if his center of mass rises about 4.0 m durblgwynp; /7;. on*rs 1 se*masing the jump?    J

  A 1200-kg car rolling on a horizontal surfr7zpt9-p(kh ssrs jj;g(()zs ace has speed v = 65 km/h when it strikes a ho-tzhj(9 rpzr ;p skgs)s js((7rizontal 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 from the4 +gj ;q twwtnf/sk )k8jf4uf: ground so it is 2.20 m above the ground. What is the t:ut )g+4/jfknk wsfq48; f jwpotential 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 ox32i8e exf s9rd 2y3jand climbs to the top of a 3300-m p2 j9o8xrisd fyee323xeak.
(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 enh+:2 -,4ulagy2cyvi dov/bf z d of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the:-2 +gio4vf yhb yud,c/z2 alv end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, issj 4ignk -ep:x8f4r(s running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she-s 8si:g4(p4 rejx nfk swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides d-k8z-fdqhn pn .p:/ ozown 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 frictionle6p1ioh.wg4 8wus4g oi ss 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 grz4y3)67edae a yoy *quavitational potential energy without the aid of a pole. With what minimum speed must Fran leave 4)y aqo dze6y3y*ua e7the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwarf qlwl ec 6atuge::+cd;4jl0/+yi5 bm d from the top of a platform with a sw ibm: l+6/u0yg;c fdql 5jea4:c+letpeed 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), whog+x* k3(x0+he4lc z4r nlzgn dse spring stiffness constant is 950N/m is attach c03+enz4x*h zgr gndl+l(4kx ed to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along tus*q ny91(, ai bh2gewhe looped track shown in Fig. 6–39. If the block is to remain on the track, (,i9ws2b1 uahg yenq* 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 a y6mt4m4ep 8fbttached to the end of a spring (spring stiffness constant k), Fig. 6–444bf 86meymtp 0. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungeeytna.rn;;bj5 cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assrt5 .;ybn;njauming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up tocy1xr vhv;- agke;b g45 y1l:z point 1 where it is released from rest. Assuming no friction, calculate the speed at poihxgz1vkyye45 a -g:l 1vbr;c;nts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s ahpb;5qwjr0r *y g(6 gbt an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevator shamg( x46f, crlfft. 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 passenf 6cm fg(4lrx,gers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends tow+2cd9 kp/8lhle nhk: 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 mhe0c 9 q6e+5k; ex5ty o)8uyf.lrgm.)akwvgof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and ) rt;y5akvc qg 5xyeueofm)g.w +e6. h8km09lcome to rest. How much thermal energy is produced 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 k(rqum*9+iki0ggixn y*8ue68 s r k-rwith a speed of 2.2m/s How mucmir grqi+x*( ngr8*u i06k89s eykk-uh thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 2j3ct -l:;j..idbm uvm2 $^{\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 treeigwerl2 7.b ,q 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, and it bounces b)i xavc3l1 nq*ack to a height of 1.5 m. in3xc*q a1)lv
(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 pul 23tv0ul( (u7wk+xca5d2qzty -l gcz tled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the nexc qg av-yt3du 7txc+lz0kz 2(u( lt52wt 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 a5 zmp02g8tayh speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it r0y5gtza 2mh 8peach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12;*r)any 8i-e,f1m ccckru3v ann1vf *m/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 block is firmly attache8 wsou x(i/1wnd 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 u si(xnw 1w/o8of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6–gjyk(8md6ya10l zy 1 sex3dp) 40. The block can slide 8pesdm31a ydgj0)yx1yzl(k6 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 equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle usncg+5vy1nxm*t) x9 lw ed a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. Txlctx1wn 95 gv*)yn m+he 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 motor to lift 2j p5j /e(3k)7xlhcn8rfoqki a 315-kg piano to a sixth-story window 16.0 m aboi3kjen c8x p27fhrkq)(5 l/ ojve?    s

  If a car generates 18 hp w9s9,1yd.emvo /x u .sdgvu qp/hen traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resistancem/uqxpdsoev.9.9y sv gu/ 1,d?    N

  A 1400-kg sports car accelerates from restosg:ajv9/bz 5+98d fzifa+ uv to 95km/h in 7.4 s. What is the average power delivered by the enojb/fi5d + + 9gzfz sv8u:v9aagine?$\approx$    hp

  (a) Show that one British hoz *xvwip-r j7,p* :jxvrsepower$ \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 f w/p00j pygazzz9yu .9orm of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg carbre5n5w 8 enk- slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is rbw5 5kn8een-needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do info1 0qd/w6 i5 vnhau bgo3otf9,dy /:v 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest emu.xl33 nguai2/wv : to 14m/s If this motion takes 1.5 s, what average power was d3/ xe.a :3ugvniu2lmweveloped?$\approx$    W

  A pump is to lift 18.0 kg of water p+ g)o /hho:kecer minute through a height of 3.60 m. What output rating (watts) should the pump motor he)oc/: hhg k+oave?    W

  During a workout, th+ fr,i,r*p g5nni s5hse football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of snr 55si*fn +gi ,hr,p32 $^{\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 clime4ida 6n 2ba-jb 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 can it climvj4 clx0 o flhuau:,v7b-69dv b at vuhlvldv6 -co7x :9fa,j0ub4a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must v3ib 5cdcrt1x0jh34 ua motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictionv3b c4xu5cih0jt31rd is 0.45?    hp

  A bicyclist coasts dow( n ab/(qoi.2av.dy rtn 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) bump8b6y yis r7vh. bwj6ytozz+ 34ers” 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 thayvb7.6itz 4owzrs by+ 8 hy36jt 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 fj)tio2 iue-3 first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a m2- )tj3uefi oiass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Oweny b-nv n*)ae2us’s famous long jump (Fig. 6–42) in the 1936 Olympics shows thaa)eyvbn 2-n*ut his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slid+j) minc zse sk1x-00oing without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top 1zx - nsij e+)cmso00kof 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 37ei3 t082qszfrn+ w np.0 m after jumping from 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 his terminal velocity was 35m/s estima r p2zf.3n+e nswiq8t0te
(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 o1oefb+a5 kct )f length L whose other end is fixed (Fi+5o catf)kb e1g. 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 top of a 3700-m-high moubt fdgv 8s9gox2,il(4ntain. The climb is made in 5.0 h statg2 fxs od9g4ilvb( ,8rting 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 rx-lbmm:i3 1cis 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts calwllbp - , :ee btss:6f8ejn3pod/0w 7igx41bn move 47,000 people per hour. If the average lift carries people about 200 m (vertically) hib1nw7 bs4s3dfe 8l- ppxeiljgew :lbt ,0:6/ogher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 65lgjnyzr(d .3. 0kg/s and falls vertically 81 m before striking the turbine blad rgy.dnz3.( jles. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), thb3r3d. q2aqzf e 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 qf3q32dr.az b 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 could convert a candy ba2fm wq vzpj:g1pzg17: r directly into work, how high could an 82-kg man climb a ladder pg1 zzq:7fjp:vg1m w2 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 anglf)c cho1m 4:hue 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 ins1j w 5ciznqx+79(sw teide 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 scale read at ittz5(cq +sewn9 x 7j1wis peak?    N

  A 65-kg student runs at 5m/s grabs a rope,(( ;3wlrmixtj and swings out over a lake (Fig. 6–45). H((lr x3imw jt;e releases 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 m*7xh),kuk:. tmeby za vertical distance of 5.0 m in 9.0 s. What minimum,)z bht u kx*7:eyk.mm power output was used to accomplish this feat?    W

  Some electric-power compz1*pze9kc+7 qmjm (hganies use water to store energy. Water is pumped by reversible turbine pumps from a low to a hig(zczh kg97+q *m1jpmeh 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 i:inva--1e 6t ogu*w rconstant k is cut in half. What is the spring stiffn nio6v-g t-uar i1*e:wess constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m, hj3twg d fwfwb+x2cu5 0)9jy 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 fr7u 4vw7nr2 2u2m zb d6ib6qlfxom 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h 6 dbq l6xn2mwui ub4z72v7fr2Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funct:o5*w aw egjg5vo 6t6hion (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the powv6 e*65:jog w tahw5oger 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 vertically liu d3h5oub7j 9 r)b3uupward a distance of 500 m, what was its vo3u75bbu ul9) 3hdrj ielocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a lb w5joml j-4hor2xn44vs 7x1)c)aqz height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide jbvjm q5sx)2h 4 7wol)zo41 ac rl4xn-electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s