A trolley weighing 30 kg moves evenly and rectilinearly on a smooth horizontal surface at a speed of 2 m / s.

A trolley weighing 30 kg moves evenly and rectilinearly on a smooth horizontal surface at a speed of 2 m / s. On the go, a bag weighing 10 kg is placed on it. How much will the speed of the cart change?

mt = 30 kg.

Vt = 2 m / s.

mс = 10 kg.

ΔV -?

ΔV = Vt – V, Vt is the speed of the cart before putting the bag, V is the speed of the cart with the bag.

To solve this problem, we will use the momentum conservation law.

Before the interaction, the impulse of the system Pm consisted only of the impulse of the moving cart: Pm = mt * Vt.

When the bag is put down, the impulse of the P system will consist of the impulse of the bag and the trolley: P = (mt + mc) * V.

According to the law of conservation of momentum, the momentum of the system does not change: Pm = P.

mt * Vt = (mt + mc) * V.

V = mt * Vt / (mt + mc).

V = 30 kg * 2 m / s / (30 kg + 10 kg) = 1.5 kg.

ΔV = 2 m / s – 1.5 m / s = 0.5 m / s.

Answer: the trolley speed will decrease by ΔV = 0.5 m / s.