On an ice skating rink, a girl of mass 50 kg stands stationary, face to face with a boy of mass 80 kg. The children push off of one another, and the boy moves away with a velocity of +3 m/s.

What is the final velocity of the girl?

–1.9 m/s
+1.9 m/s
–4.8 m/s
+4.8 m/s

- 4.8 m/s is the final velocity of the girl.

Option C

Explanation:

Momentum is the amount of movement of a moving body, measured as the product of mass (m) and speed.

In this given case, the total and initial momentum are zero. According to the conservation of Momentum, the push before and after should be equal. Therefore, framing the equation as below

But here, the push off by the children is opposite to each other (one is positive and other one is negative).

Given data:

m of girl = 50 kg

m of boy = 80 kg

after push off, v of boy = 3 m/s

we need to find v of girl

By substituting the given values in the above equation, we get

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