A 100 kg train traveling at 20 m/s crashes into a stationary 400 kg car.
After the collision the car and the train are stuck together. What is
their velocity.

common velocity V = 4 m/s

Explanation:

Given that a 100 kg train traveling at 20 m/s crashes into a stationary 400 kg car.

Since both of them were stuck together after collision, the collision is inelastic.

The formula for inelastic collisions is:

M1U1 + M2U2 = ( M1 + M2 )V

We are told that the second car is stationary.

Therefore, U2 = 0

This will reduce the equation to:

M1U1 = (M1 + M2)V

Where V = common final velocity

M1 = 100 kg

M2 = 400 kg

U1 = 20 m/s

U2 = 0

Substitute all the parameters into the equation

100 × 20 = ( 100 + 400 ) V

2000 = 500V

Make the V the subject of formula

V = 2000/500

V = 4 m/s

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.