A rigid horizontal smooth rod AB of mass 0.75 kg and length 40 cm can rotate freely abput a fixed vertical vertical axis through the midpoint O. Two strings each of mass 1 kg initially at rest are placed at a distance of 10 cm from O on either side of the rod. The rod is set in rotation with an angular velocity of 30 radian per sec and when the rings reach the ends of the rod, the angular velocity in rad/sec is?
Asked by nasir.mirza
13th June 2018,
10:07 PM
Answered by Expert
Answer:
To solve this question, we need to use conservation of angular momentum.
Initially two rings(hope two rings, not two strings as given in the question ! ) are at 10 cm from mid point.
Moment of inertia I1 of the combined rod and rings at inititial time is given by
Moment of inertia I2 of the combined rod and rings when the rings are at end position is given by
By conservation of angular momentum, we have 
, where ω1 and ω2 are initial and final angular speed of rotation.
, where ω1 and ω2 are initial and final angular speed of rotation..03 × 30 = .09×ω2 ; hence ω2 = 10 rad/s
Answered by Expert
15th June 2018,
12:48 PM
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