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Phy 121
Your 'cq_1_24.2' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_24.2_labelMessages **
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: ->->->->->->->->->->->-> :
yes the law of conservation of momentum says that the momentum before the collision must be equal to the momentum after the collision
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That is a good statement of the law, but it doesn't guarantee that the law applies to this collision. One condition of the law is that the system must be isolated, with no external forces. So if momentum isn't conserved, we know that the system isn't isolated.
To rephrase the present question, then, is the system isolated?
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• What would the marble velocity have to be in order to exactly conserve momentum, assuming the steel ball's velocities to be accurate?
answer/question/discussion: ->->->->->->->->->->->-> :
m1v1 + m2v1 = m1v2 + m2v2
(60 g) * 80 cm/s = 60 g * 50 cm/s + 20 g * v2
4800 gcm/s = 3000 gcm/s + 20v2
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Good equation. That's 90% of the battle.
Can you now solve it to find v2?
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10 min
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