Question

A disc of mass m and radius r is gently placed on another disc of mass 2m and radius r. The disc of mass 2m is rotating with angular velocity `omega_(0)` initially.
The disc is placed such that axis of both are concident. The coefficient of friction is `mu` for surfaces of contact Assume that pressure on disc is uniformely distributed.

Time elapsed in this process
A. `(omega_(0)R)/(mug)`
B. `(2omega_(0)R)/(mug)`
C. `(omega_(0)R)/(2mug)`
D. `(omega_(0)R)/(4mug)`

Answer 1

Correct Answer - B
`sigma=(-((Deltar)/(r)))/(((Deltal)/(l)))`
`(DeltaA)/(A)=(2Deltar)/(r)=-2%implies ((Deltar)/(r))~=-1%`
`sigma=-(((Deltar)/(r)))/(((Deltal)/(l)))`
`(0.4) =-((-1%))/(((Deltal)/(l)))implies ((Deltal)/(l))=(10)/(4)% " "(Deltal)/(l)=2.5%`