IIT JEE , AIEEE Forum - Physics , Mechanics

kishan12

For these types of problems we use Constraint relation which is based on the fact that the length of the string remains constant.
we measure the length of the string from a refrence points like centre of a pulley or any fixed point.

In this problem let the distance from B to A pulley be x .and the distance b/w puuley A and mass M be y.

Therefore 2x+y=constant as the length of the string will always be constant.
Differentiating this equation twice w.r.t time we get
2a'+a=0
where a' is the acceleration of the pulley B and hence the block 2M and is that of string which passes over pulley A and hence mass M.
so a'=-a/2.
Hope you got it.

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