Question

Two blocks (mass M and 2 M) are placed on a horizontal frictionless surface connected by an ideal spring. Initially, everything is at rest and there is a string compressing the mass-spring system from equilibrium. At some time after the string is cut, the block of 2M mass reaches its maximum kinetic energy of 20 J. What maximum kinetic energy does the block of mass M attain?

• A. 10 J
• B. 20 J
• C. 40 J
• D. 30 J

Answer 1

The correct option is C 40 J

applying conservation of momentum
$K_{2M}=\frac{p^2}{4M}=K=20$
$K_M=\frac{p^2}{2M}=2K=40$