In still water, a swimmer swims at a speed of 2 m / s. When it is sailing upstream of the river, its speed relative

In still water, a swimmer swims at a speed of 2 m / s. When it is sailing upstream of the river, its speed relative to the bank is 0.5 m / s downstream. What is the current velocity?

V = 2 m / s.

Vpt = 0.5 m / s.

Vt -?

According to the law of relativity of motion, the speed of a body relative to a stationary frame of reference V is equal to the sum of the speed of movement of a moving frame of reference relative to a stationary Vпн and the speed of a body relative to a moving reference system Vтп: V = Vпн + Vтн.

The swimmer’s speed in still water V is the speed of the body relative to the moving frame of reference Vtn: V = Vtn.

The flow velocity Vt is the speed of the moving frame of reference relative to the stationary Vpn: Vt = Vpn.

The swimmer’s speed against the current Vпт is the speed of the body relative to the stationary frame of reference V: V = Vпн.

Vpt = Vt + V – vector.

Since the speed of the current is directed in the opposite direction of the swimmer’s movement, then Vпт = – Vт + V.

Vt = V – Vpt.

VT = 2 m / s – 0.5 m / s = 1.5 m / s.

Answer: the current speed is Vt = 1.5 m / s.