Puck A, of inertia m, is attached to one end of a string of length , and the oth

Question

Puck A, of inertia m, is attached to one end of a string of length , and the other end of the string is attached to a pivot so that the puck is free to revolve on a smooth horizontal surface. Puck B, of inertia 12m, is attached to one end of a string of length /4, and the other end of the string is attached to a second pivot so that B is also free to revolve. In each case, the puck is held as far as possible from the pivot so that the string is taut and then given an initial velocity v perpendicular to the string.

PART A

How does the magnitude of the angular momentum of puck A about its pivot compare with that of puck B about its pivot?

PART B

How does the rotational kinetic energy of A compare with that of B?

Explanation / Answer

a) In case m = J
2E1 = J1*1^2 = m*(V/)^2
2E2 = J2*2^2 = 12m*(V*4/)^2
E2/E1 = 12^2 = 144

b) In case m = mass
2E1 = J1*1^2 = m*^2*(V/)^2 = mV^2
2E2 = J2*2^2 = 12m*^2/12*(V*4/)^2 = m^2*12V^2/^2 = 12mV^2
E2/E1 = 12

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