# A person walks at a speed of 5 km / h relative to the train carriage against the direction of travel

**A person walks at a speed of 5 km / h relative to the train carriage against the direction of travel; the train moves at a speed of 20 km / h relative to the Earth. With what speed the person is moving relative to the ground.**

Vh / n = 5 km / h.

Vp / s = 20 km / h.

Vch / s -?

The speed of a person relative to the stationary coordinate system Vh / s is equal to the sum of the speed of the person relative to the moving coordinate system Vch / n and the speed of the moving coordinate system relative to the stationary coordinate system Vp / z.

Vch / s = Vch / n + Vp / s.

Since the train and the person go in opposite directions, then Vch / s = Vch / n – Vp / s.

Vh / h = 5 km / h – 20 km / h = – 15 km / h.

Answer: a person walks in the direction of movement of the train with a speed of Vch / h = 15 km / h relative to the ground.