In what ways is the word “work” as used in everlr kj+o2: j-)j/nmf lryday language the same as that defined in physics?ol rn j-2+l)j/mjfr :k In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explain. ztx+9zw5z dq5

Can the normal forcegi 88i w.z(zwo on an object ever do work? Explain.

A woman swimming upstream is not moving with respect to szk z8ep:yd; 4the shore. Is she doing any work? If she stops swimmingz4 ze pdksy;8: and merely floats, is work done on her?

Is the work done by kinetic friction forces always negat-, pd5 :ef(hcr tjzas1ive? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under the-5sa zh :(ejd 1ftp,rcm.]

Why is it tiring to push hard against a solid wall e p7sg1phpgc6( ven though you are doing no workpg1 7(h6 pgspc?

You have two springs that are identical except that p u;4ae2gmj.ispring l is stiffer than sprin.jmapu 42; iegg 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 fo xyw0 9a3u3evkb1 xy(orce on a block that is free to slide on a frictionless surface (Fig.6-30). The bloco0exy3b(wv9u3 ka x1yk 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 y*ltd8im qp9jp0 te,2eou jumpl 8t pm 2jtd,eie9q0*p as high as you can?

In Fig. 6–31, water balloons are tossed from the roof: eun t6 3 s-0-9srkn *ocbop1bnua1od of a building, all with the same speed but with different launch angles. Which one has the highest speed on impan1u9cnnrtokp3o 1uos6:0 bdsb--e* a ct? Ignore air resistance.

A pendulum is launched f hcv7070qz ,r8k c6 jttflm1sprom a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along thzv00fc1mrt7,h 7jt kc 6s8pq le 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 4ivhetb7a 5hug .09tscompress the spring by pressing down with your hand at7 asiu btg 095v.4hhend then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel pi0(nf0d s tr2wire (Fig. 6–33). The instructor pulls the ball back and stands against their0d (2f n0pst 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 0.hx 7b vqmfyom/2rx-auni.2 g lzop 50)htg+the top of a waterfall fx0a q2iruobv.g f75m+)/g m o hx2zhpl.-t0 nyalls to the pool below?

Describe the energy transformations when a child hops are5-,e8 v;gceugnmy( bb vmv,2t 44jk lound on a pogo stick.

Describe the energy transformations that take place when 0shm;u *vs)tro(fed1 a skier starts skiing down a hill, but after a time is broughs 1sr (0m*ftehoudv); t to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a 7aqzcg 1bvxkm: 8vhme* 8hou+r wui,u+4n 5y6hill of 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, and (b) there is friction (deep sn wu+vg* u16yhi:7co8h zrv,85n x+mkbm4qaueow)?

Seasoned hikers prefe)qf+( jygs/xc 5t3ydd r to step over a fallen log in their path rather than stepping on top(q5+xs3/j tcfgd ) yyd and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the o 0spt slh+5epph, e1 *n1esam2ther, are fired into a bale of hay. Assuming the hay exerts a ph10m1,psa+e5nslpes eh2 *t 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 termsna 3+ll (ge) mo/1sjbj of energy, (a) ignoring friction, and (b) taking frisem1a(+bg/ol) 3 njjlction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height8oz4 g1w zv, qao0mr5;1bhqmx greater than its original height?gqzoxzmr,5ov 8ma10wq;41 hb Explain.

Suppose you lift a suitcase from thhqujacts:08sr.r r,/2m/ q p me 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 . uj2 r mr c8,sm:0/hqtrqsa/palong 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 tij0t 6b1hq quba(or4 r.4lz6hhe power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cl7 n1d wuf embk4: tf-yal+;t)simb straight up; -y:mt+1 t7f a4nb dfleswu)k?

Recall from Chapter 4, Example 4–14, that you bfz i d3fjwk6.j1d/ 8jg 9:k yhdple+)can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every63l1 k /z+depjd:wy)g kbjj d98f h.fi 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 gbwdi,-*sh-p;4cl q nrravitational force when a 265-kg pile driver falls 2.80 m? bqn ,;chpd i4 s-wl*r-   J

  A 65.0-kg firefighter cliapr.wov r5q -e:;yf6 mmbs a flight of stairs 20.0 m high. How much work is require6;.awref y v:mpr- q5od?    J

  A 1300-N crate rests on the floor. How much work19;qf- rrsl31rseiw3 j5mykt 9efh)w is required to move it at constant lreysfjrhi3 1 kt1e39qr)fm s;ww5-9speed (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 1,7 wdrm rlqv.30.3 m across a rough floor without acceleration, if t37m,dl qv.rr whe effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a fo)-2lst2sh9gzu8oumiz;8z sdrce across a floor at a rate of for 7.0 s. Findlsi2ozs29d u- ms8z u) th;8zg the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tabledpqj ynzz7 yl rh.le46.w71o /. How much work is required to sypj14. 6/yrl 7 h. ezozldwqn7tack them one on top of another?    J

A lever such as that show5cvmt,k( l5-fupy6koc uhm*5 n in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio ofu 56oh,t -mcf l*(5pcuykmkv5 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 isi3zmz21 k n7gps+aq*5c4nmlr kept from accelerating by a man who is pushing back on it parallel to the rq ms kla14iz*c+73 g z5nnpm2incline (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 accefe *)als*78ucn ek-cy9 gr -celeration of 0.108ke uacn- esf*lrg)c9 e7y-c* 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/ul//zwr yg*a linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x ku1awk3db l 97jco.*s axis, varies as shown in Fig. 6–37. Determine the work done by this forccu .9 * 3ska7bdj1kolwe to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerte-(f:o* d.c67czixr:zxjd fs ud 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 0y*m;o e c-k:d+noufmmolecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its spe2,hhr)esmz dxl vz;o.(e-c 5azgvt 91ed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop aopq8iw g ):1h +1yt kkb:0sfhdn electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105km/h6ugc9f4;jlyujq8 :cv ?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average fo i9 l3rj9koiu3rce of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as r3 iojlu993ik it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves afmskwge.71z j5rc 2w-.v9c /.bik sc k fielder’s glove backward 25 cm when the ball is caught. What was the average fkwk.5is9r e 1csgc m.kw7.j/v2b-fczorce exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by nf) np7g l )/b(tdj)jbwhat factor will its minimum braking distance be increase) 7 dnj)(n/pfj)bgtbl d, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s l;irf52 gyc5tskid 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 cc l525g r;iytfar 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 the pjpuw38t. jiy,d (h3lhlate, it may have slowed by 10%. Neglecting gravity, h w l( hjp8y3i,3t.udjestimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up bhe ce go9+(i8xq1c 4cky someone who does 80.0 J of work on it? Neglect air resistan 1 8eq+ cx94gk(icochece.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sing 7;ty *2:bqkoe.6 xhw-ybhgqwle cable. Deter.q7w;wxkth6g b -ob*:ehq y y2mine
(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 thisug 9x q8*i lg7xk5ur2;6y ciaq spring7c5 i;ur gxa u2qk l98*x6ygiq be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. 2 ; k 4btu8r4qq:kbegaWhat is the change in pote:qe 44gb b uqakr;8k2tntial energy?    J

  By how much does the gravitati*6+m-joz d/hji5no yl onal potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0o hy6i/ld5* oz mj-+jn m during the jump?    J

  A 1200-kg car rolling on a horizontal sur10 2 mjcxo j)tkt+b )fejouh90face has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spr x 20u)o+ ) 0ojtebhk9m1jtfjcing stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so io+bb4db6y 31 x*lvz zvt is 2.20 m above the ground. What is the potential energy of the book relative tby1 vz3obd z4x+*l6 bvo
(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 eg in7/bhw:*i cckx)t *levation of 1600 m and climbs to the top of a 3300-m peakwn7*xbikgh c):/ *t ci.
(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 uu8fsfq. 99w ,:n.zoxfkg3iv of the spring is next to the 15-cm mark on tof nv x.8z kgi.: w9su9ff3,quhe ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine han c;h:t6oqd/vf u/k d3rging vertica d3q/v/6:cu;okf d rthlly from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down mk5 4kxnu4cqwtb0 2: f -7svoma 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 2z65ygs30zlkx; 4nf6uo jqtybme3 7)go8 mi +b8.0$^{\circ}$ 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’sh+6+ m2gr hdbm9ub1 1/xypz sk7+ emlk kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and 1m9z26lmp/sk h+ k17+begh+byrmudx cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of azv g0564uaeo( rg3o lh platform with a speed of h04 (r3u oglzve ao5g65.0 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 1 in zw2 rs+c,e47wafpmass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it 7rz w2, +4wepacinsf1 give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown 47k.rov nv84qlejmi(n0btz)9y)pt kh- *t j bin Fig. 6–39. If the blockk-bhipttzk e )qr4)v mn7(nl* vt jb4 .8jy9o0 is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (sp y.v dmf+uuqh9k ni *ce-gsj:e);-s9l2k5s vhring stiffness constant k), Fig. 6–40. The block is given an initial displaceqfg );u-9hle 9y2s hv5s* +k-:kemi. scd vnujment $x_0$ 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 ju8f7aou 7ts8nmm/uj v; mps from a bridge. She is tied to a bungee cord whose unstru 87an7t;/moj msfv8uetched length is 12 m, and falls a total of 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 in Fig. 6–41 is dragged up to poibolq y(86-v qqnt 1 where it is releqo-86v q qb(ylased 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 thrown with a seyh476* ldjp. c yvu+qpeed 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 a sm96i x,ezc0jhnpv t-) pring 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 tha9cie , -zjnxv) t0p6hmt passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cgg5hzhi. oz,l7x ic( o;lw8 +aycle 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 )q 6.mqqj 2issin opposite directions, collide head-on and come to rest. How much thermal eq.6ijqss)mq 2 nergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high7 vdqu: ta1*q1hqf j7i and reaches the bottom with a speed of 2.2m/svt *uq:d7h7j fa1qiq1 How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest anw7gdc- 2)f ;daoes /nwz mh96gd 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 dropped fromrrw5*x r7mwq3 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 hei zy mkj 7p:*b.u;gmt2oght of 2.0 m, and it bounces back to a height of 1.5 m.mb.*:k;p2y u oztj mg7
(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 hcd3lri+4g gh2 orizontal force of 350 N. F2r4i3+dhl gc gor 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 coas,zk5haq b/4ilugm 9wak* :k-t ter in Fig. 6–41 passes point 1 with a speed of If the average force /k kmza9h wgtiu*l ,-k5ab:q4of 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 my3*n 2 ;p+uwy zk+(onbn)k p5m5yrag foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very ukoe)mgw t+x*d 6s2l+cb0k b5light 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 coefw2 g)k+ eb05cx*lbsu+dmo tk 6ficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a vet pdbk72-ilt zk :6va/ry light horizontal spring, Fig. 6–40. The block can slide along a table i2dka-7k:tl6zvbt / p 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 3 l0gl5* cq0kjisp19y.ax tjjspace shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would it0.iq*jj cyl as0ljtk9 p31 gx5s 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 f3naskmt1:w8jcp r+5p :2 6hz2pfo be1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 mkof2 bh65+t : w:pjnmpr32sfec8p1az above?    s

  If a car generates 18 hp3r-oa kg,:ap y when traveling at a steady 88km/h what must be the average force exerted on the car due to friction and 3gap:, o-ykarair resistance?    N

  A 1400-kg sports car accelerates from rest to 9gnpfv5sacy t1093; p i5km/h in 7.4 s. What is the average power delivered by i5tanv013 g yp;p 9csfthe engine?$\approx$    hp

  (a) Show that one Britix) ubq5u3gzrcd4g9g l+ 1qfv +sh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilqi, :ixpr 50*5rqdn umowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in aboutnk q d7aat;7s (nznf vch,h9;( 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car trave( nt (7qaaznnf,h;d9c;ks vh7ling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.5vx1urb0( dzr2f0 xpu 0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to h r1)(0kx42trc5tpl9lwaqr g,c.ymsy e (l a(14m/s If this motion takes 1.5 s, what average power was dmy(h9 ), llras g42p.talkq(ycew5(x 1 r rc0teveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throughdhcvxr xi 7+ji7*g ; i80cmroglgb194 a height of 3.60 m. What output rating (watts) should the pump moi+8i rx7c;1gcdlo gmv9h74bi j r x*0gtor have?    W

  During a workout, the football players at State U.4v.ycq ,2(a cpvuha5b ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined atvy u4c2ah qpv(ca.5,b 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 g. ye2u py-mx2a 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 hiv rsm- h rht+-2b ia0c6zpm):mq1y7xy ta, 0dqll can it climb at a constant speed of 75km/h if the frictional forces add up totr-7yqacd0hvi mr 1yp:60-ab+ ztq )2,xm smh 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kgfii n;d d:+ajk2b paq4l;;e;u box along a lev2i;ui4a:j;+dpf;a le qknd b;el floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.r ,- o3rody( ibd/wgz*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) bumpers” that are designed u:.lz 6kmg2dyto compress andmu l g:z.dky26 rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the;3- tgx, :xno .eabxkl ground, and the remaining four shelves are each spaced 30.0 cm above the prev :lxxg;naeob.,k3-x tious one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owen a9 8qb*vv6u/kyouy6g s’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of th *uygavo66u98 bvk/y qe 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 vdn x-o;69sxv;3pjvg along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at thjx vspg n;3vxvo9 d-;6e 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 afte31 jyic ge/4skr jumping from an aircraft without his parachute opening. He landed in a j/ckeys 3g1i4snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(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 weydsm-z p hy/*nj23 g,hose other end is fixed (Fig. 6–43). y-njg2*dzpm,yehs 3/
(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-h 7b) +-4j vo0a lkvw (,,cqlil(ex*rph:inarsigh mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calcux: 0r , +boal*jvq 4s i(cvnwpilhe-) lk,(ra7late
(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 elevatocy95ecp ;;s7kc oua yhi6-x)c 4jpb8vr is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can movq./ qeubub*l, e 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powerq/uqu b* ,e.bl needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650y1l6zu;mo f h j-s146wg kj.kn91xgcjkg/s and falls vertically 81 m before strizw mj;cu j1xs1h16nj6ylf4 g.k9 k-go king 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 2 uhgi8:k;y raa circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and rhygau:8i; k2the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convi*eaeoz788 ,c i q9usfert a candy bar directly into work, how high could an 82-kg man climuf8 oiae,7 c*qe9z8sib a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle o6y4qtdx2dbo ( f 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses*oz9so2gu/,w.x uexbt eh ) +b 0.60 mm, and it tells you your weight is 710 be+ uw9huo2te,zg b* o.sxx/ )N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs atgjp uj wzvke*56;uqw8vzxkf98 : 5e6w 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope whz;z9wjvufwxw 6v8qu*j:gp5ke86 5ke en his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vapr 5id wiar5/;2q6y: l us3bbertical distance of 5.0 m in 9.0 s. What minimum power output was usep2q sdia; bba l/:6urr35yi5 wd to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rezn1ilaws)+:s versible turbine pumps from a low to a high reservoir. To store the energy produced innazs +s :)wl1i 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 5iah3u5q /5geekzol :9vrt.nin half. What is the spring stiffness constant for each of teu tovnh r/i.5q zge55al3 k:9he two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3p9g*f yrddym, /kokgb5p6. /z 7 $^{\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 3.2epgn / a36hn.h0++ wbvy+vtd i s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stw0e h vdt.v6n+a i/++ nb3yphgays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “8l lfpxxt,6 tw7f;g-estress test”), the patient walks on an 678wlxxpgt f ftl,;-einclined treadmill (Fig. 6–46). 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 vertically upward a distance of 500 m 6w5umbc okuwws380b:pl*iu- , what om l*w :0u ubbw 5spc38-6uwkiwas its velocity 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 height of 2.0 m at a rate575:8hfw krbfw+ vbq l of 95kg/s (a) If this water wheel is set up to proviw8 7l:q5krhf5b vw b+fde electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s