Elastic Collision: Finding Velocities After Collision

[Chica1975]

Homework Statement

a 5.00g object moving to the right at 20.0cm/s makes an elastic head-on collision with a 10.0g object that is initially at rest. Find the velocity of each object after the collision.

Homework Equations

p=mv
m1v1 +m2v2/m=m1=m2

The Attempt at a Solution

I have attempted this question several times.

I have converted all units to kg and m/s before starting all calculations.
I found the momentum for each using p=mv but this was not the right answer.
then I tried the other equation I have given and tried to minus the initial velocity from answer - still its not correct.

I am not great at collisions and find these really difficult - esp the conservation of energy/momentum concepts. I don't know to translate the conceptual into the application using equations and the info given in the question.

Please someone help me.

 

[tiny-tim]

Hi Chica1975!

I have converted all units to kg and m/s before starting all calculations.
I found the momentum for each using p=mv but this was not the right answer.
then I tried the other equation I have given and tried to minus the initial velocity from answer - still its not correct.

I am not great at collisions and find these really difficult - esp the conservation of energy/momentum concepts. I don't know to translate the conceptual into the application using equations and the info given in the question.

In collisions, momentum is always conserved.

In collisions, energy is never conserved unless the question says so … in this case it does, because it uses the word "elastic".

You always need two equations to solve a collision question … one is always conservation of momentum, the other is either conservation of energy or some other constraint like "perfeclty inelastic" or " coefficient of restitution = 0.5".

So here you'll need both of the conservation equations …

show us your full calculations, and then we'll see what went wrong, and we'll know how to help! ​