Question

Two blocks, of mass $1\, kg$ and $2\, kg$ respectively, are connected by a spring and kept on a frictionless table. The blocks are pulled apart, so that the spring is stretched, and released from rest. At a certain instant of time, the block of mass $1 \,kg$, is found to be moving at a speed $2 \,m / s$. What must be the speed of the other block at this instant?

• A. 1 m/s
• B. 0.5 m/s
• C. 4 m/s
• D. 0.25 m/s

Answer 1

Answer: (A)

1 m/s

Answer 2

According to conservation of linear momentum $0=m_{1} v_{1}+m_{2} v_{2}$ $0=1 \times 2 \times 2 \times v^{2}$ $v_{2}=-1 m / s$ Negative sign shows that $2\,kg$ is pulled in a opposite direction to that of mass $1 \,kg$ .