A person is walking from the front of a train toward the back of a train at a constant velocity of 3 mph. The train is moving forward at a velocity of 20 mph. What is the velocity of the walking person relative to the land outside the train?

Explanation:

This is the Galilean transformation.

V' = V - U   where want to find V' in the primed frame of reference.

The primed frame is moving at speed U = -20 relative to the train.

V = -3 is the speed of the person in the frame of the train.

Then V' = -3 - (-20) = 17 mph relative to the land outside the train.

b) phosphorus pentoxide

it is the second option.