How can I solve for the mass of the first car in an elastic collision problem?

[tony873004]

In an elastic collision problem, I'm supposed to solve for the mass of the 1st car (m1). I get stuck here. How do I re-write this to solve for m1?

$$u_2=\frac{2*m_1v_1}{m_1+m_2}$$

 

[whozum]

Thats the equation for an inelastic collision, but

$$u_2m_1+u_2m_2-2m_1v_1 = 0$$

$$u_2m_1 - 2m_1v_1 = -u_2m_2$$

$$m_1(u_2 - 2v_1)= -u_2m_2$$

$$m_1 = \frac{-u_2m_2}{u_2-2v_1}$$

 

[tony873004]

Thanks, whozum. That worked !