Question

Two blocks of masses 10 kg and 20 kg are connected by a light spring as shown. A force of 200 N acts on the 20 kg mass as shown. At a certain instant the acceleration of 10 kg mass is 12 $m{s}^{-2}$.

• A. At that instant the 20 kg mass has an acceleration of 12 $m{s}^{-2}$
• B. At that instant the 20 kg mass has an acceleration of 4 $m{s}^{-2}$
• C. The stretching force in the spring is 120 N
• D. The collective system moves with a common acceleration of 30 $m{s}^{-2}$ when the extension in the connecting spring is the maximum.

Answer 1

The correct option is B At that instant the 20 kg mass has an acceleration of 4 $m{s}^{-2}$

Hence,

Option $B$ is correct.

For $10kg$: $T=ma$

$=10\times 12$

$=120N$............(1)

For $20kg$ $F-T=ma$

$200-120=20\alpha$

$80=20a$

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

$\therefore$ acc of $20kg=4m{s}^{-2}$