Rotation 5 Question 17

29. When discB is brought in contact with discA, they acquire a common angular velocity in time t. The average frictional torque on one disc by the other during this period is

(a) 2Iω3t

(b) 9Iω2t

(c) 9Iω4t

(d) 3Iω2t

(2007, 4M)

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Answer:

Correct Answer: 29. (a)

Solution:

  1. Let ω be the common velocity. Then from conservation of angular momentum, we have

(I+2I)ω=I(2ω)+2I(ω)ω=43ω

From the equation,

angular impulse = change in angular momentum, for any of the disc, we have

τt=I(2ω)I43ω=2Iω3τ=2Iω3t



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