Question

The masses of 10 kg and 20 kg respectively are connected by a massless spring. A force of 200 N acts on the 20 kg mass. At the instant shown, the 10 kg mass has an acceleration of $12{ms}^{-2}$, what is the acceleration of 20 kg mass?

• A. $12{ms}^{-2}$
• B. $4{ms}^{-2}$
• C. $10{ms}^{-2}$
• D. None of these

Answer 1

The correct option is B $4{ms}^{-2}$

Let $F$ be the force of the spring acting between the blocks.

From the FBD of Bock of 10 Kg,

$F=ma$ $\Rightarrow F=10\times 12=120N$

Let acceleration of the block of 20 Kg is $a$.

From the FBD of Block 20 Kg,

$200=ma$ $\Rightarrow 200-120=20\times a$

$\Rightarrow a=4m{s}^{-2}$