# Optics (Reflection of Light)

1. Jul 29, 2014

### DriggyBoy

A gun of mass 'M' fires a bullet of mass 'm' with a horizontal velocity 'v'. The gun is fitted with a plane mirror facing towards the receding bullet. Find the velocity relative to its image just after the gun is fired.

2. Jul 29, 2014

### Orodruin

Staff Emeritus
The above is simply the problem statement. What are your thoughts on the problem? Where do you get stuck?

3. Jul 29, 2014

### DriggyBoy

Cannot proceed much....law of conservation of momentum needs to be applied i guess

4. Jul 29, 2014

So apply it and show what you get.

5. Jul 29, 2014

### DriggyBoy

I have solved but not sure if its correct. I have considered the velocity of the gun to be M. Now by conservation of linear mmntum, mv=MV.....therefore V = mv/M
relative velocity wrt gun = v + V = mv/V + v = (m/M + 1)v
Therefore relative vel wrt image = 2*v(m/M + 1) = 2v(m/M + 1) [ since image dist = objct dist for plane mirror ]
Not sure....just check it.....thanks in advance :)

6. Jul 29, 2014

### Staff: Mentor

That's the general idea, but you would lose marks for lack of rigor (and multiple typos!).

mv = -MV