Question

The block of mass $m$ is at rest just before the collision.
What is the total kinetic energy of the blocks just AFTER the collision, if the collision between them is elastic?

• A. $16J$
• B. $32J$
• C. $64J$
• D. $128J$
• E. $256J$

Answer 1

The correct option is D $128J$

For a elastic collision, the kinetic energy after collision $=$ the kinetic energy before collision

$=\frac{1}{2}\left(4\right)(8{)}^2+\frac{1}{2}(m\left)\right(0{)}^2=128J$