# Determine the speed of a boat with a mass of 240 kg, moving without a rower at a speed

Determine the speed of a boat with a mass of 240 kg, moving without a rower at a speed of 1 m / s, after a weight of 80 kg has dropped out of it.

According to the law of conservation of momentum, the equality is true:

v1 * (M + m) = v2 * M – v1 * m, where v1 and v2 are the speed of the boat before and after the drop of the load, M is the mass of the boat, m is the mass of the cargo.

Let us express from the above equality v2:

v2 = (v1 * (M + m) + v1 * m) / M.

v2 = v1 * (1 + 2m / M).

Substitute the given values:

v2 = 1 * (1 + 2 * 80/240) = 7/4 = 1.75 m / s.

Answer: the required speed was 1.75 m / s.

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