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A force acts on a 30 gm30 \text{ gm} particle in such a way that the position of the particle as a function of time is given by x=3t4t2+t3x = 3t - 4t^2 + t^3, where xx is in metres and tt is in seconds. The work done during the first 4 seconds4 \text{ seconds} is:

A

5.28 J5.28 \text{ J}

B

450 mJ450 \text{ mJ}

C

490 mJ490 \text{ mJ}

D

530 mJ530 \text{ mJ}

Step-by-Step Solution

Given, mass of the particle, m=30 gm=30×103 kg=0.03 kgm = 30 \text{ gm} = 30 \times 10^{-3} \text{ kg} = 0.03 \text{ kg}. The position of the particle is given by x=3t4t2+t3x = 3t - 4t^2 + t^3. The velocity of the particle is the rate of change of position: v=dxdt=ddt(3t4t2+t3)=38t+3t2v = \frac{dx}{dt} = \frac{d}{dt}(3t - 4t^2 + t^3) = 3 - 8t + 3t^2

Initial velocity at t=0 st = 0 \text{ s}: vi=38(0)+3(0)2=3 m/sv_i = 3 - 8(0) + 3(0)^2 = 3 \text{ m/s}

Final velocity at t=4 st = 4 \text{ s}: vf=38(4)+3(4)2=332+48=19 m/sv_f = 3 - 8(4) + 3(4)^2 = 3 - 32 + 48 = 19 \text{ 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=KfKi=12mvf212mvi2W = \Delta K = K_f - K_i = \frac{1}{2} m v_f^2 - \frac{1}{2} m v_i^2 W=12m(vf2vi2)W = \frac{1}{2} m (v_f^2 - v_i^2) W=12×0.03×(19232)W = \frac{1}{2} \times 0.03 \times (19^2 - 3^2) W=0.015×(3619)=0.015×352=5.28 JW = 0.015 \times (361 - 9) = 0.015 \times 352 = 5.28 \text{ J}

Thus, the work done during the first 4 seconds4 \text{ seconds} is 5.28 J5.28 \text{ J}.

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