Question

I know the answer but can someone please, please explain?

Two blocks are on a frictionless surface and have the same mass m. Block 2 is initially
at rest. Block 1 moves to the left with speed 4v. Block 1 collides elastically with block 2.
What is the final speed of block 1?
The answer is 0 and I cannot for the life of me figure out why.

Answer 1

Step-by-step explanation:

The only explanation I can think of is this:

Block 1 is moving to the left and strikes Block 2, which is at rest. 100% of the momentum of Block 1 transfers to Block 2. So Block 2 now moves to the left at 4 m/s (you didn't specify a unit) and Block 1 comes to a complete stop and is now at rest.