 #1
PSN03
 100
 9
 Homework Statement:
 A block of mass m is attached to one end of a light string which is wrapped on a disc of mass 2m and radius R. The total length of the slack portion of the string is l. The block is released from rest. The angular velocity of the disc just after the string becomes taut is:
 Relevant Equations:

Conservation of angular momentum
Initial angular momentum=final angular momentum
Moment of intertia about disc about centre is given by MR²/2
I was first wondering wether we can solve this question by applying conservation or energy or not but after googling it I found that we can't apply conservation of energy since there will be some energy lost in this case. I don't know how this energy is getting lost.
My second doubt was if we apply conservation of angular momentum about centre of the disc then won't there be a torque due to the string? So it won't be valid to use conservation of angular momentum.
Can anyone please clarify these doubts.
My second doubt was if we apply conservation of angular momentum about centre of the disc then won't there be a torque due to the string? So it won't be valid to use conservation of angular momentum.
Can anyone please clarify these doubts.