# Homework Help: Collisions in 1 dimension

1. Nov 27, 2004

### disruptors

On a frictionless horizontal air table, puck A (with mass 0.366 kg) is moving toward puck B (with mass 0.254 kg ), which is initially at rest. After the collision, puck A has velocity 0.119 m/s to the left, and puck B has velocity 0.655 m/s to the right.

What was the speed of puck A (Vai) before the collision?

K I put v=v1(m1+m2)/(m1-m2)

v1=-.119 m/s since it moves in the left direction and i defined right as +ve

my initial velocity of puck a came to be -0.659 m/s, but it seems to be wrong.

Calculate , the change in the total kinetic energy of the system that occurs during the collision.

for the KE I got 0.333 J but I don't know why its wrong
thx guys

Last edited: Nov 28, 2004
2. Nov 28, 2004

### zoetrope

???

Since puck B is initially at rest, the initial linear momentum of the system is: m1*v

After the collision, the linear momentum will be equal to: m1*v1 + m2*v2

Since linear momentum is conserved, the initial and final linear momentums will be equal. Once you equate these, you can solve for v.

Hope this helps,

zoetrope

3. Nov 28, 2004

### disruptors

yeah that helps thanks

i was looking at it as an inelastic collision

for the energy part i am using the equation

1/2 m1 v1(squared)i = 1/2 m1 v(squared)1f + 1/2 m2 v(squared)2f

question is looking for change in kinetic energy DURING collision

i calculated Final KE - Initial KE but is that not considered the total change in KE DURING the collision?