A phonograph record is dropped onto a freely spinning turntable. Then: neither a

Question

A phonograph record is dropped onto a freely spinning turntable. Then: neither angular momentum nor mechanical energy is conserved because of the frictional forces between record and turntable the frictional force between record and turntable increases the total angular momentum the frictional force between record and turntable decreases the total angular momentum the total angular momentum remains constant the sum of the angular momentum and rotational kinetic energy remains constant Block A, with a mass of 4 kg, is moving with a speed of 2.0 m/s while block B, with a mass of 8 kg, is moving in the opposite direction with a speed of 3 m/s. The center of mass of the two block-system is moving with the velocity of: 1.3 m/s in the same direction as A 1.3 m/s in the same direction as B 2.7 m/s in the same direction as A 1.0 m/s in the same direction as B 5.0 m/s in the same direction as A

Explanation / Answer

45) Ans D = the total angular momentum remains constant.

46)

PCM = PA + PB = mAvA + mBvB = (4kg)(2m/s) + (8kg)(-3m/s) = -16 kg· m/s

PCM = (mA+mB)vCM = (-16 kg· m/s)

vCM = (-16 kg· m/s) / (mA+mB)

vCM = -1.33 m/s

Ans:- B) = 1.33 m/s in the same direction as B

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