A raft weighing 120 kg is floated along the river, it moves evenly in a straight line and in 10 minutes passes 300 m

| December 12, 2020 | education

A raft weighing 120 kg is floated along the river, it moves evenly in a straight line and in 10 minutes passes 300 m relative to the coast. Determine the speed and direction of the raft after a 65 kg boy jumped off it at a speed of 1 m / s relative to the shore. Consider cases where: a) the boy jumped in the direction of the raft; b) the boy jumped against the direction of the raft

V current = V raft = 300/600 = 0.5 m / s
Raft impulse = m * v = 120 * 0.5 = 60 kg * m / s
Boy’s impulse = 65 * 1 = 65 kg * m / s
In the first case, P = p1 + p2 = 65 + 60 = 125 kg * m / s.
This is the total impulse, then V = P / M = 125 / (120 + 65) = 0.68 m / s
In the second case, the boy will change the direction of movement of the raft, because his impulse is greater
P = p1-p2 = 65-60 = 5 kg * m / s. Then the speed is 5 / (120 + 65) = 0.028 m / s



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