Question

The masses of $10\text{kg}$ and $20\text{kg}$ respectively are connected by a massless spring in fig. A force of $200$ newton acts on the $20\text{kg}$ mass. At the instant shown, the $10\text{kg}$ mass has acceleration $12{\text{m/sec}}^2$. What is the acceleration of $20\text{kg}$ mass?

• A. $4{\text{ms}}^{-2}$
• B. $3{\text{ms}}^{-2}$
• C. $2{\text{ms}}^{-2}$
• D. $1{\text{ms}}^{-2}$

Answer 1

The correct option is A $4{\text{ms}}^{-2}$

Force on $10\text{kg}$ mass $=10\times 12=120\text{N}$
The mass of $10\text{kg}$ will pull the mass of $20\text{kg}$ in the backward direction with a force of $120\text{N}$.
$\therefore$ Net force on mass $20\text{kg}=200-120=80\text{N}$
Its acceleration $a=\frac{\text{force}}{\text{mass}}=\frac{80\text{N}}{20\text{kg}}=4{\text{m/s}}^2$