Question

A train car with mass m1 = 550 kg is moving to the right with a speed of v1 = 7.2 m/s and collides with a second train car. The two cars latch together during the collision and then move off to the right at vf = 4.7 m/s.3)What is the change in kinetic energy of the two train system during the collision?

Answer 1

kfinal-kinitial = magic!

Answer 2

I'm assuming the second train car has a velocity of 0. So its kinetic energy is 0. So using the equation 0.5*m*v^2. The change in kinetic energy is: kf-ki = 0.5*(m1+m2)*vf^2 - 0.5*m1*v1^2. You can solve for m2 using inelastic collision conservation of momentum. m2 = 292.5kg
So, 0.5*(550+292.553)*4.7^2 - 0.5*550*7.2^2 = -4950J