question_answer

Two blocks, of mass \[1\text{ }kg\]and \[2\text{ }kg\] 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 \[1\text{ }kg,\] is found to be moving at a speed\[2\text{ }m/s\]. What must be the speed of the other block at this instant?

A)  \[1\text{ }m/s\]           

B)  \[0.5\text{ }m/s\]

C)  \[4m/s\]           

D)  \[0.25\text{ }m/s\]

Correct Answer: A

Solution :

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