A girl riding a bicycle along a straight road
Question:

A girl riding a bicycle along a straight road with a speed of 5 m/s throws a stone of mass 0.5 kg which has a speed of 15 m/s with respect to the ground along her

direction of motion. The mass of the girl and the bicycle is 50 kg. Does the speed of the bicycle change after the stone is thrown? What is the change in speed, if

so?

Solution:

Given,

m1 = 50 kg

m2 = 0.5 kg

u1 = 5 m/s

u2 = 5 m/s

v1 = ?

v2 = 15 m/s

From the law of conservation of momentum,

Initial momentum = final momentum

(m1 + m2) u1 = m1v1 + m2v2

Substituting the values, we get

v1 = 4.9 m/s

Therefore, the speed of cycle and the girl decreases by: 5 – 4.9 = 0.1 m/s.

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