Question

A 1.0-kg block and a 2.0-kg block are pressed together on a horizontal frictionless surface with a compressed very light spring between them. They are not attached to the spring. After they are released and have both moved free of the spring
1. the lighter block will have more kinetic energy than the heavier block.
2. the magnitude of the momentum of the heavier block will be greater than the magnitude of the momentum of the lighter block.
3. the heavier block will have more kinetic energy than the lighter block.
4. both blocks will both have the same amount of kinetic energy.
5. both blocks will have equal

Answer 1

Answer:

4. both blocks will both have the same amount of kinetic energy.

Explanation:

When the blocks are released free from the compression force, the spring exerts equal and opposite force on each block but the block with heavier (double) mass will attain slower ( half ) speed as compared to the lighter block according to the law of inertia. This works in synchronization to energy conservation.

Spring force is given as:

$F=k.\Delta x$

where: $\Delta x=$ length of compression in the spring

We know kinetic energy is given by:

$KE=\frac{1}{2} m.v^2$

Hence the kinetic energy of both the blocks is equal when they are released to move free.