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course Phy 121
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:
m1 = 60 g * 0.001 kg/g = 0.06 kg
v1 = 80 cm/s * 0.01 m/1 cm = 0.8 m/s
v2 = 50 cm/s * 0.01 m/1cm = 0.5 m/s
m2 = 20 g * 0.001 kg/g = 0.02 kg
v1 = 0 m/s
v2 = 70 cm/s * 0.01 m/1 cm = 0.7 m/s
total momentum before = 0.06 kg * 0.8 m/s + 0.02 kg * 0 m/s
total momentum before = 0.048 kg m/s + 0
total momentum before = 0.048 kg m/s
total momentum after = 0.06 kg * 0.5 m/s + 0.02 kg * 0.7 m/s
total momentum after = 0.03 kg m/s + 0.014 kg m/s
total momentum after = 0.044 kg m/s
It is about the same.
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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:
It would have to be moving slightly faster. 0.9 m/s.
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