Cracking the SAT Physics Subject Test

collision, the speed of block m is 4 times the speed of block M.

10. What is the speed of block M after the collision?


11. Is the collision elastic?

Here’s How to Crack It

10. If we let V′ be the speed of block M immediately after the
    collision, then the speed of block m will be 4V′. By applying
    conservation of linear momentum, we find that

Therefore, the speed of block M immediately after the collision

is 2 m/s (and the speed of block m immediately after the

collision is 8 m/s).

11. A collision is elastic if the total kinetic energy is conserved.
    Since