# Problem involving momentum

1. Mar 11, 2012

### Mdhiggenz

1. The problem statement, all variables and given/known data

The nucleus of Po^214 decays radioactively by emitting an alpha particle (mass 6.65×10−27 kg) with kinetic energy 1.16×10−12 J, as measured in the laboratory reference frame.

a) 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.

2. Relevant equations

3. The attempt at a solution

My approach to the problem was using the fact that K1=K2

I then solved for Vf by doing the following

k1=1/2mvf2

squareroot(2k1/m)=vf

squareroot[2(1.23*10^-12j)/(6.65*10^-27kg)]= 1.92*10^7

What I am confused about is my books solution manual does something else aswell they use the following formula after they acquire the value above: mfvf+mnvn=0

They solve for vn and get

vn=[(6.65*10^-27)/(3.50*10^-25kg)]*1.92*10^7=3.65*10^5

I dont understand how they get 3.50*10^-25, and why its necessary to solve for vn.

Thank you

2. Mar 11, 2012

### SHISHKABOB

it would seem that 3.50*10-25kg is the mass of the daughter nucleus, which is then nucleus left behind when the alpha particle is emitted. Did they not give you this information? Do you have any way of determining the mass of the daughter nucleus?