Question

A train car with mass m₁ = 550 kg is moving to the right with a speed of v₁ = 8.5 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 v_f = 5.2 m/s.

What is the mass of the second train car? kg Submit 3) What is the change in kinetic energy of the two train system during the collision?

Answer 1

Momentum equals mass times velocity.

The momentum of the first car can be calculated as (550)(8.5)= 4675 kg*m/s

To find the mass of the second train car, you have to set up an equation for conservation of momentum. Split the problem into two parts--Before the collision, and after the collision.

Before= the momentum of the first train car= 4675
After= the momentum of the combined cars= (550+m2)(5.2)

Now, set the before and after equal to each other.

4675=(550+m2)(5.2)
=>m2= 349.04 kg

So, the mass of the second car is 349 kg

The change in kinetic energy can be defined as the kinetic energy after- the kinetic energy before
So, since kinetic energy equals 1/2mv^2, the change is--

1/2(349.04+550)(5.2)^2-1/2(349.04+550)(8.5)^2

So, the change in kinetic energy is 20323 N.