Phy 231
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A steel ball of mass 60 grams, moving at 80 cm / sec, collides with a stationary marble of mass 20 grams. As a result of the collision the steel ball slows to 50 cm / sec and the marble speeds up to 70 cm / sec.
Is the total momentum of the system after collision the same as the total momentum before?
answer/question/discussion: We have initial momentum of ( 0.06 kg * .8 m/s) + (.02 kg * 0 m/s) = 0.048 kg*m/s, and final momentum of ( 0.06 kg * .5 m/s) + (.02 kg * .7 m/s) = (0.03 kg*m/s) + (0.014 kg*m/s) = 0.044 kg*m/s; therefore, the total momentum before is greater than the total momentum after the collision.
What would the marble velocity have to be in order to exactly conserve momentum?
answer/question/discussion: Since the steel ball still has a momentum of .03 kg*m/s we find the the momentum of the marble must be .048 kg*m/s - .03 kg*m/s = .018 kg*m/s; therefore, the marble would need a velocity of (.018 kg*m/s)/(.02 kg) = 0.9 m/s
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&#Very good responses. Let me know if you have questions. &#