You are Here: Home >< Physics

# Help me solve this tricky momentum question in my physics test? watch

1. So I had a physics test today on momentum circular motion and electric fields and capacitance and one of the questions was as follows

An alpha particle is emitted from a polonium nucleus at a speed of 8 × 10^7. The masses of the alpha particle and nucleus are 4.002 and 212 respectively. Calculate the recoil velocity of the nucleus.

Can someone solve it and tell me the answer?
2. (Original post by lolatmylifeee)
So I had a physics test today on momentum circular motion and electric fields and capacitance and one of the questions was as follows

An alpha particle is emitted from a polonium nucleus at a speed of 8 × 10^7. The masses of the alpha particle and nucleus are 4.002 and 212 respectively. Calculate the recoil velocity of the nucleus.

Can someone solve it and tell me the answer?
Would it help you if I told you the particle and the nucleus were both at rest to begin with?
3. There's Zero Momentum before so there must be zero after so 0= m1v1 +m2v2 so sub in the mass and velocity values And you can get the recoil velocity
4. (Original post by Protostar)
Would it help you if I told you the particle and the nucleus were both at rest to begin with?

The question was exactly how I typed it can u tell me the final answer so I can cross check with what I wrote? Thanks
5. (Original post by M4cc4n4)
There's Zero Momentum before so there must be zero after so 0= m1v1 +m2v2 so sub in the mass and velocity values And you can get the recoil velocity
Can u solve and tell me what answer u got I want to cross check with what I had written as the answer thank you
6. (Original post by lolatmylifeee)
The question was exactly how I typed it can u tell me the final answer so I can cross check with what I wrote? Thanks
Show us your working so far - just posting answers isn’t really the policy around here, sorry!
7. (Original post by Protostar)
Show us your working so far - just posting answers isn’t really the policy around here, sorry!

The value for speed I gave in the orginal question is not exact bc I can't remember the exact value but it was something similar. Anyway what I did was :

Recoil velocity of Nucleus = (4.002 × (8×10^7)) divided by (4.002+212)
So according to the values I used on TSR and in the above eqn I'm getting 1482208ms-1 as the recoil velocity
8. (Original post by lolatmylifeee)
The value for speed I gave in the orginal question is not exact bc I can't remember the exact value but it was something similar. Anyway what I did was :

Recoil velocity of Nucleus = (4.002 × (8×10^7)) divided by (4.002+212)
So according to the values I used on TSR and in the above eqn I'm getting 1482208ms-1 as the recoil velocity
I’m not sure your m2 is correct. It seems to me as though the mass of the nucleus includes the mass of the particle, i.e. that is the mass of the nucleus before the particle is emitted. Therefore your m2 would be (4.002 - 212)?

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: October 22, 2017
Today on TSR

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University