Chapter 5 Circular Motion
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11. An object moving in a circle at a constant speed is:
A. accelerating in the direction of motion.
B. accelerating toward the center of the circle.
C. accelerating away from the center of the circle.
D. not accelerating because its speed is constant.
explanation: The acceleration is always perpendicular to the velocity because it does not change the speed of the object, but only its direction.
12. A CD has a diameter of 12.0 cm. If the CD is rotating at a constant angular speed of 200 revolutions per
minute, then the tangential velocity of a point on the circumference is:
radius, r = ½ diameter = 0.06 m. angular velocity,
= 200 x (2
)/(60 s) = 20.94 rad/s. Then v =
r = 1.26 m/s.
15. A CD has a diameter of 12.0 cm. If the CD is rotating at a constant frequency of 4.00 cycles per second,
then the tangential velocity of a point on the circumference is:
v = 2
f r = 1.51 m/s.
19. A 4.00 kg mass is moving in a circular path of radius 2.50 m with a constant angular velocity of 5.00 rad/s.
The centripetal force on the mass is:
F = m
2
r = 250 N
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26. A 0.500 kg stone is moving in a vertical circular path attached to a string that is 75.0 cm long. The stone is
moving around the path at a constant frequency of 2.20 rev/sec. At the moment the stone is overhead, the stone
is released. The magnitude and direction of the velocity of the stone when it leaves the circular path is:
A. 10.4 m/s horizontal.
B. 10.4 m/s vertical.
C. 22.0 m/s horizontal.
D. 22.0 m/s vertical.
The velocity will be the same as just before it was released, which is v =
r = 2
f r = 10.4 m/s. Since it was overhead the direction is horizontal.
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 Fall '09
 ZHIXIANZHOU,
 Circular Motion, 4.0 cm, 6.0 Rad, D. Quadruples, 6 rad, 8.0 rad

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