How to Calculate the Alpha Particle's Velocity After Collision?

[cheater1]

A proton with initial kinetic energy (5.2 MeV) collides with an alpha particle (initially at rest). The collision is perfectly elastic and the proton travels off at an angle of 133o relative to its initial direction. What is the velocity of the alpha particle after the collision? Assume the alpha particle has four times the mass of a proton.

My teacher made this problem but I'm trying to solve it and I need final velocity to find the answer and its not given.

 

[Bob S]

You have 3 unknowns:

1) Final proton energy
2) Final alpha energy (or velocity)
3) Final alpha angle

But you also have 3 conserved quantities. Can you name them?

Bob S

 

[cheater1]

You have 3 unknowns:

1) Final proton energy
2) Final alpha energy (or velocity)
3) Final alpha angle

But you also have 3 conserved quantities. Can you name them?

Bob S

kinetic, momentum , can't think of the last one.

 

[fizzynoob]

you only need conservation of momentum

 

[cheater1]

you only need conservation of momentum

I don't know initial and finial speed.

 

[Maybe_Memorie]

I don't know initial and finial speed.

You know kinetic energy, you should know the proton mass, so you can compute initial velocity.

 

[Bob S]

You have 3 unknowns:

1) Final proton energy
2) Final alpha energy (or velocity)
3) Final alpha angle

But you also have 3 conserved quantities. Can you name them?

kinetic, momentum , can't think of the last one.

Momentum is a vector quantity. Does this help?

Bob S