# Calculate the impulse exerted after an inelastic collision

marsupial

## Homework Statement

A block A of mass m traveling with speed v collides head-on with a stationary body B of mass 2m. The two bodies stick together. Calculate the impulse exerted by body B on body A during the collision.

## Homework Equations

## J = p_{final} - p_{initial} ##
## p_{initial} = p_{final} ##

## The Attempt at a Solution

I am not sure if this is correct. First I considered the system of the two blocks to calculate v':
mv + 0 = 3mv' -> v' = v/3

Then I calculated the initial and final momentum of block B on A using v' for final velocity:
## p_f - p_i = 2mv/3 - 0 = 2mv/3 ##

But I don't feel confident in the answer.

Homework Helper
Gold Member
But I don't feel confident in the answer.
Newton's third law of motion implies that the blocks should experience "equal but opposite" impulses during the collision. How does the impulse delivered to A compare to the impulse delivered to B in your solution?

Does that boost confidence?

marsupial
marsupial
It's -2mv/3, so it appears to be consistent. Thank you. Physics induces a great deal of uncertainty in me!

Homework Helper
Gold Member
Physics induces a great deal of uncertainty in me!
You're not alone. (I think Heisenberg said something similar.)

Vibhor