# Finding the angle of impact

1. Jul 29, 2014

### bobie

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

A ball A hits another ball B 3 times more massive and rebounds at an angle λ = 43°.1..... (cosλ =5/√52).

Can anyone determine the angle of impact? is it possible , at all?

Last edited: Jul 29, 2014
2. Jul 29, 2014

### Simon Bridge

Depends on the context. i.e. what is the angle with respect to?
You'd usually want to use conservation of momentum - which means you need more than one momentum vector.

3. Jul 29, 2014

### bobie

The angle of impact λ is the angle made by the trajectory of ball A with the line joining the centres of mass of the two balls CA-CB

Last edited: Jul 29, 2014
4. Jul 29, 2014

### haruspex

You've already used λ for the rebound angle. Call it something else.
So draw yourself a diagram of the impact, invent symbols as necessary for the masses, velocities and angles, and write down the equations for conservation of momentum in the co-ordinate directions.

5. Aug 4, 2014

### bobie

Isn't there a formula to find directly one angle knowing the other one?
It shouldn't be difficult to work one if in principle it is possibel to find it, right?

Thanks for four help

6. Aug 5, 2014

### Simon Bridge

Yes there is - however, it is poor practice to do physics by memorizing formulas: there are just too many of them.
It is much better to get into the habit of deriving your formulas from the physics in front of you.

Besides, giving you the formula, in this case, would amount to "doing your homework for you"; which we like to avoid.

7. Aug 5, 2014

### haruspex

That should result from the momentum equations. Write them out, solve them, post how far you get.

8. Aug 5, 2014

### bobie

Hi Simon, it is not homework (no school) , as usual I am speculating. I was just wondering why it is never mentioned.

I'll work out the formula by myself, it shouldn't be difficult.
Thanks