Two bodies A and B each of mass m are fixed together by a massless spring . A force F acts on the mass B as shown in fig .3 (a)18. At the instant shown , the body A has an acceleration a What is the acceleration of B ?

Explanation

Let T be the tension in the string . Equation of motion of A is T= m a if a' is acceleration of B , the equation of motion of B can be written as
`ma = F - T = F - ma`
`:. a' = (F/(m-a))`