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Question

A particle of mass 0.2 kg (initially at rest) starts moving in one dimension under a force that delivers a constant power 0.5 W to the particle. Then the speed after 5 seconds is

A
20 m/s
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B
5 m/s
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C
10 m/s
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D
20 m/s
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Solution

The correct option is B 5 m/s
Given, Mass of the particle m=0.2 kg
Power P=0.5 W
Initial speed u=0 m/s

We know that, Power P=F v
[when force and velocity are in same direction]

P=ma×v=mvdvdt
0.5=mvdvdt [P=0.5 W, given]
or mv dv=0.5 dt
Integrate on both sides,
v0mv dv=500.5 dt
[let velocity after 5 s be v]
mv22=0.5×5
v=0.5×5×20.2
v=5 m/s

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