A body of mass 5kg is thrown vertically upwards from ground with a velocity of 20ms−1. What will be its momentum just before hitting the ground? Assume upward direction as positive.
A
−100kgms−1
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B
0kgms−1
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C
100kgms−1
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D
−20kgms−1
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Solution
The correct option is A−100kgms−1 Given: Mass of the body, m=5kg and upwards velocity, u=20ms−1. We know that v2=u2−2as Here, displacement of the body, s=0, acceleration, g=−9.8ms−2 ∴ Velocity of the body just before hitting the ground, v=202−2×(−9.8)×(0) ⇒v=√202 Since upward direction is taken as positive, v=−20ms−1 We know, momentum, p=mv=5×(−20)=−100kgms−1.