# Collision with spring

kle89
Problem

One block (3kg) is moving at 8m/s on a frictionless plane to collide with another block at rest with the same mass, but has a spring in front of it. Spring constant = 6 N/m

a. Determine the maximum distance the spring is compressed.
b. Determine the final velocities of the blocks after the collision. You should assume that the 1 kg and 2 kg blocks remain stuck together.

Honestly i have no idea how to set the equation up? Would i use 1/2mv^2' = 1/2kx^s + 1/2mv^2 to find the distance of the spring? The problem is i wouldn't know what the final velocity would be after hitting the spring so i can't solve exactly for x. Also the other block with the spring could move after the collision so wouldn't its velocity be equal to that of the original block after hitting the spring but in the opposite direction? Any hints to get me on the right track would be appreciated. Thanks in advance.

## Answers and Replies

abm4life
maybe you can assume that at the point where the 1st block contacts the spring of the 2nd block, the velocity of the 1st block is still 8 m/s... Then you can just look focus on the time frame in which the whole spring compression occurs, knowing that the initial velocity of the 1st block when it contacted the spring was 8m/s.

Part b would most probably involved conservation of momentum law. But you need to solve a.

Last edited:
tim_lou
use center of mass frame!