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Question
A particle of mass m moves with a variable velocity v, which changes with distance covered x along a straight line as v=kx,where k is a positive constant . The work done by all the forces acting on the particle, during the first t second is
Options:
A .  mk4t2
B .  mk4t24
C .  mk4t28
D .  mk4t216
Answer: Option C
:
C
GIven v=kx or dxdt=kx or x12dx=kdt
Integrating both sides, we get
x1212=kt+C; Assuming x(0) = 0
Therefore, C = 0
2x=ktx=k2t24 or v=k2t2
Therefore, work done,
W = Increase in KE
= 12mv212m(0)2=12m[k2t2]2=mk4t28

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