Given, mass of the particle, m=30 gm=30×10−3 kg=0.03 kg.
The position of the particle is given by x=3t−4t2+t3.
The velocity of the particle is the rate of change of position:
v=dtdx=dtd(3t−4t2+t3)=3−8t+3t2
Initial velocity at t=0 s:
vi=3−8(0)+3(0)2=3 m/s
Final velocity at t=4 s:
vf=3−8(4)+3(4)2=3−32+48=19 m/s
According to the work-energy theorem, the work done by the net force is equal to the change in kinetic energy :
W=ΔK=Kf−Ki=21mvf2−21mvi2
W=21m(vf2−vi2)
W=21×0.03×(192−32)
W=0.015×(361−9)=0.015×352=5.28 J
Thus, the work done during the first 4 seconds is 5.28 J.