9. A man, holding a weight in each hand, stands at the center of a horizontal fr
ID: 1484000 • Letter: 9
Question
9. A man, holding a weight in each hand, stands at the center of a horizontal frictionless rotating turntable. The effect of the weights is to double the rotational inertia of the system. As he is rotating, the man opens his hands and drops the two weights. They fall outside the turntable. Then: A his angular velocity doubles B. his angular velocity remains about the same -C. his angular velocity is halved D. the direction of his angular momentum vector changes E. his rotational kinetic energy increases 10. Two pendulum bobs of unequal mass are made of perfectly elastic material. They are suspended from the same fixed point by strings of equal length. The lighter bob is drawn aside and then released so that it collides with the other bob on reaching the vertical position. What quantities are conserved in the collision? A. Both kinetic energy and angular momentum of the system B. Only kinetic energy C. Only angular momentum -. D. Angular speed of lighter bob E. None of the aboveExplanation / Answer
Please post question #10 and #2 separately. I am providing answer here for question #9
Answer #9
When released weights do not fall vertically. As the weights are dropping, there is no torque applied on the man or the weights hence angular momentum of the system is conserved. This can be realised by visualising that the weights are still a part of the system, they are just no longer in the man's hands. Also, rotational inertia is conserved, hence the angular velocity of the system remains about the same.
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