# What type of collision?

## Homework Statement

Block A is moving to the right at 2 m/s when it collides with an identical block B that is initially at rest. After the collision, block A is moving back to the left at 1 m/s and block B is moving to the right at 3 m/s. Which answer best describes the type of collision that occurred?
a) elastic
b) inelastic
c) perfectly inelastic
d) The answer to this question depends on the precise masses of the two blocks.
e) This question cannot be answered with the given information.

## Homework Equations

(m1)(v1i) = (m1)(v1f) + (m2)(v2f)
KE = (1/2)mv^2

## The Attempt at a Solution

my teacher said the answer was a, but i thought that the answer would be e, because the initial KE of the system is 2m, while the final KE is 5m. this means an increase in KE but i dont know if increase in KE can still be considered elastic.

Last edited:

Andrew Mason
Science Advisor
Homework Helper

## Homework Statement

Block A is moving to the right at 2 m/s when it collides with an identical block B that is initially at rest. After the collision, block A is moving back to the left at 1 m/s and block B is moving to the right at 3 m/s. Which answer best describes the type of collision that occurred?
a) elastic
b) inelastic
c) perfectly inelastic
d) The answer to this question depends on the precise masses of the two blocks.
e) This question cannot be answered with the given information.

## Homework Equations

(m1)(v1i) = (m1)(v1f) + (m2)(v2f)
KE = (1/2)mv^2

## The Attempt at a Solution

my teacher said the answer was a, but i thought that the answer would be e, because the initial KE of the system is 2m, while the final KE is 5m. this means an increase in KE but i dont know if increase in KE can still be considered elastic.
I agree with you. Energy has been added. But we don't know how much energy was added. We don't know if the collision was inelastic (it lost 1m of energy, say) and that energy was replaced plus additional energy (4m added) or if it was elastic and 3m of energy added.

Note: This could be a collision between two blocks with already compressed springs. Upon the colliding, the springs release and push the two blocks apart with spring force.

AM