Question

Two identical blocks of mass 0.5 kg each are shown in figure. A massless elastic spring is connected with A. B is moving towards A with kinetic energy of 4J. Match following two columns. Neglect friction.

Answer 1

$\frac{p^2}{2m}=KE$;
$\therefore p=\sqrt{2m\ast KE}$;
$\Rightarrow p=\sqrt{2\ast 0.5\ast 4}=2$ kg m/s
Hence option (A)$\to 3$;
Since block A is at rest initially, $p_{cm}=p_B=2$ kg m/s
Hence option (B)$\to 3$;
At max compression of the spring, the velocities of both blocks are same.
$\therefore$ momentum of both blocks will be same and each will be half of the momentum of $p_{cm}=\frac{2}{2}=1$ kg m/s;
Hence option (C)$\to 2$;
In elastic collision between two equal masses, velocities are interchanged. So, B comes to rest and A starts moving.
Hence option (D)$\to 1$;