Question

Two railroad freight cars with masses 110 Mg and 150 Mg approach with equal speeds of 0.310 m/s . They collide, the lighter car rebounding opposite its original direction at 0.270 m/s.

Find the velocity of the heavier car after the collision. Assume the original direction of the lighter car is positive. Express your answer to two significant figures and include the appropriate units.

What fraction of the original kinetic energy was lost in this inelastic collision?Express your answer using two significant figures.

Answer 1

I am calculating -.28 m/s for the 1st part but it is not correct.

Answer 2

Lets pick the original direction of the light car as positive. Before
110*.31 - 150*.31 = -12.4
That momentum must be conserved
After
110(-.27) + 150vf = -12.4