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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/sGiven, 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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