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High School Physics BLOG - online class notes

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September 18, 2019

Solution to problems – class 9 – Set 1 Q 55

Problem Statement

55) A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank, with a horizontal velocity of 3 m/s. With what velocity does the boat begin to move backwards ?


As no initial velocity is given in the problem statement, we will consider it as zero.
So whatever movement the boat gets its due to the jump of the girl.

So initial momentum =0

Mass of the girl =m1 =50 kg
velocity of the girl =v1 = 3 m/s

Mass of the boat =m2 =300 kg

Velocity of the boat =v2 =?

Final momentum = m1v1 + m2v2 =50 x 3 + 300 v2

As per the law of conservation of momentum,
150 + 300v2 = 0

Or, v2 = -150/300 = -0.5 m/s

The negative sign indicates that the boat go backwards

Question Set – Physics Problems for grade 9

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