physics-speed

i need help with this one
thanks

A particle starts from rest and is acted on by a net force that does work at a rate that is proportional to the time t. The speed of the particle is proportional to:

a. sq. root t
b. t
c. t^2
d.1/sq. root t
e. 1/t



Work done is proportional to the integral of a constant times t. That means the work done is proportional to t^2. It will equal the final kinetic energy, which is proportional to v^2. Therefore v^2 is proportional to t^2, and v must be proportional to t.

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  1. i choose answer d.

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  2. i got the same problem, and the answer is A. I have no idea why

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  3. the answer is A
    work is proportional to t.
    work is the change in kinetic energy.
    then work is of the order of V^2.
    then V^2 is prop. to t.
    therefore, V is prop. to sq.root t

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