# Magnitude of the recoil velocity of the nucleus

1. Nov 13, 2005

The nucleus of 214Po decays radioactively by emitting an alpha particle (mass 6.65*10^-27) with kinetic energy 1.23*10^-12 J, as measured in the laboratory reference frame.

Assuming that the Po was initially at rest in this frame, find the magnitude of the recoil velocity of the nucleus that remains after the decay.

I used the kinetic energy to solve for the velocity: k=.5mv^2 which is 19233429 m/s. Now I'm not sure what to do with that. I think I'm suppose to use the conservation of momentum theory, but I don't know how.

2. Nov 13, 2005

Anyone Know?

3. Nov 13, 2005

### whozum

Conservation of momentum theory says that the net momentum stays constant if there are no external forces acting. Are there any external forces? What was the initial momentum?

4. Nov 13, 2005

No, there are no external forces. Initial momentum= mv= 19233429*6.65*10^-27= 1.27902306*10^-19

5. Nov 13, 2005

so does conservation of momentum not apply her? What do I need then to find the magnitude of the recoil velocity?

6. Nov 13, 2005

### whozum

Before the explosion the particle is at rest. What is its momentum? No external forces means momentum is conserved.

7. Oct 14, 2007

### jgibbon2

I have a problem simular to this...

in order to find the recoil velocity... i have tried v=-(sqrt KE*2m)/m .... is there a known mass for Polonium that you plug in to this problem? where am i going wrong?