August 4, 2008
PHY 2053 Discussion
Practice Exam 2 (Chapter 68)
1.
A crane drops a 0.30 kg steel ball onto a steel plate. The ball’s speeds just before impact and after are
4.5 m/s and 4.2 m/s respectively. If the ball is in contact with the plate for 0.030 s, what is the
magnitude of the average force that the ball exerts on the plate during impact? (ImpulseMomentum
Theorem)
a. 87 N
b. 133 N
c. 3.0 N
d. 3.5 N
2.
A machine gun is attached to a railroad flatcar that rolls with negligible friction. If the railroad car
has a mass of 6.25
×
10
4
kg, how many bullets of mass 25 g would have to be fired at 250 m/s off the
back to give the railroad car a forward velocity of 0.5 m/s? (Conservation of Momentum)
a. 400
b.
2 000
c. 3 000
d. 5 000
3.
In a twobody collision, if the kinetic energy of the system is conserved, then which of the following
best describes the momentum after the collision? (Collisions)
conserved
4.
A 20kg object sitting at rest is struck elastically in a headon collision with a 10kg object initially
moving at +3.0 m/s. Find the final velocity of the 20kg object after the collision. (Elastic Collisions)
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 Fall '06
 Buchler
 Physics, Angular Momentum, Kinetic Energy, Momentum, Moment Of Inertia, Rotation

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