Collisions

Question 1

For what collisions is momentum conserved?

Answer 1

All collisions

Question 2

What is the centre of mass speed?

Answer 2

(p_1+p_2)/(m_1+m_2 )
The sum of the momenta divided by the sum of the masses

Question 3

How do you go from the lab frame speeds to COM frame speeds and vice versa?

Answer 3

u=u’+v_cm
u’=u-v_cm

Question 4

What happens in a completely inelastic collision?

Answer 4

The particles stick together and remain still in the COM frame
All kinetic energy is lost

Question 5

What happens in an elastic collison?

Answer 5

Kinetic energy is conserved
In the COM frame the momenta are reversed