question_answer

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

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 kg is pulled in a opposite direction to that of mass 1 kg.