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Unformatted text preview: is KEi = 2 (5 kg)(5 m/s)2 + 1 (1 kg)(2 m/s)2 = 64.5 J. Final kinetic
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energy is KEf = 1 (5 kg)(3 m/s)2 + 2 (1 kg)(8 m/s)2 = 54.5 J
2 Page 3 5. A 2 kg block is moving along a ﬂoor with coeﬃcient of kinetic friction µK = 0.2. It has an initial speed of 4 m/s. The block slows to
a stop.
3 (a) Find the force of friction on the block. The normal force on the block due to the table is mg =
(2 kg)(9.8 m/s2 ) = 19.6 N.
FK = µK FN = (0.2)(19.6 N) = 3.9 N 4 m/s 2kg
!K=0.2 3 (b) How far does the block slide before coming to a stop? The initial kinetic energy of the block is KE = 1 mv 2 =
2
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(2 kg)(4 m/s)2 = 16 J. The friction does negative work
2
W = F ∆x on the block, and steals it all away by the time
it stops. Thus
F ∆x = 16 J =⇒ ∆x = 3 6. 3.9 N
= 0.24 m
16 J 1m A A meterstick with weight mg = 1 N balances on
two wedges as shown. What is the force exerted by the left
wedge on the meterstick? Assume the center of mass of the
stick is right in the middle.
A) 0.375 N B) 0.5 N C) 0.625 N D) 1 N 1N
0.8m Let FL and FR be the forces due to the pivots: FL + FR = 1 N. Put the pivot at the
center of mass, and the torque due to FL is τL = FL (0.5 m) clockwise and the torque
due to FR is τR = FR (0.3 m) counterclockwise. Since this is in equilibrium, the torques
must sum to zero, so
3
FL (0.5 m) = FR (0.3 m) =⇒ FL = FR = 0.6FR
5
And since FL + FR = 1 =⇒ FR = 1 − FL , FL = 0.6(1 − FL ) =⇒ 1.6FL = 0.6 =⇒
FL = 0.6/1.6 = 0.375 N Page 4 !"# $ %&'()&*+, . /,0 &1 2/(3%+ ! (4 4566 &'+/7 .8 , %(*3/ ,*7 9,./ ,4 4%&2*# :%/ 1&'9/
&* +%/ . /,0 .8 +%/ %(*3/ %,4 , </'+(9, 9&06 &*/*+ +%,+ 054+ . /= 6.
A horizontal beam of weight W is supported by a
3 7.
A horizontal beam of weight W is supported by
hinge and cable as shown. If the hinge exerts a force F on the
a hinge and cable as componentthe F is exerts a force F
shown. If of hinge
beam, then the vertical
A) on the beam, then upwards
nonzero, pointing the vertical component of F is
A) nonzero, pointing upwards
B) nonzero, pointing downwards
C) B) nonzero, pointing downwards
nonze...
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 Spring '12
 ScottHill
 Physics, Acceleration

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