Question

A train car, which has a mass of 2500 kg, is rolling along with a speed of 14 m/s. It strikes a stationary (not moving) train car, which also has a mass of 2500 kg, and they stick together. What is their combined speed after the collision?

Answer 1

v = 7 m/s

Step-by-step explanation:

Momentum of the first train car before = mass of the first train car x velocity of the first train car

= 2500 kg x 14 m/s

= 35000 kg·m/s

Momentum of the second train car before = mass of the second train car x velocity of the second train car

= 2500 kg x 0 m/s

= 0 kg·m/s

Total momentum before = Momentum of the first train car before + Momentum of the second train car before

= 35000 kg·m/s + 0 kg·m/s

= 35000 kg·m/s

Total mass after = mass of the first train car + mass of the second train car

= 2500 kg + 2500 kg

= 5000 kg

Total momentum before = Total momentum after

35000 kg·m/s = 5000 kg x v

v = 35000 kg·m/s / 5000 kg

v = 7 m/s

Answer 2

7m/s

Step-by-step explanation:

The formula for inelastic collisions is m1*v1 + m2*v2 = (m1+m2)*vf. From this question, we are given m1 = 2500kg, v1 = 14m/s, m2 = 2500 kg, v2 = 0 m/s. Plugging all this into the above equation gets 2500 * 14 = 5000 * vf. Solving that gets vf = 7m/s.