# 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.

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