The masses of `10kig` and `20kg` respectively are connected by a massless spring as shown in figure. A force of `200N` acts on the `20kg` mass. At the instant shown, the `10kg` mass has acceleration `12m//sec^(2)` . What is the acceleration of `20kg` mass?

Options

A. 0
B. `10m//s^(2)`
C. `4m//s^(2)`
D. `12m//s^(2)`

Answer

C

Explanation

Let extension in the spring Is `x` .
For `10kg` mass: `kx=10a_(1)=10xx10=120N`
For `20kg` mass: `200-kx=20a_(2)`
implies `200-120=20a_(2)` implies `a_(2)=4m//s^(2)` .