The pulley arrangement of fig. are identical. The mass of the rope is negligible. In (a) mass m is lifted up by attaching a mass (2 m) to the other end of the rope. In (b), m is lifted up by pulling the other end of the rope with a constant downward force F =2 mg. In which case, the acceleration of m is more ?

Explanation

Case (a): `a=((2m-m)/(2m+m))g`
`a=(g)/(3)`
Case (b): FBD of mass m

`ma'=T-mg`
ma'=2mg-mg
`rArr ma'=mg`
a'=g
So in case (b) acceleration of m is more.