Consider that the system shown below is released from rest. The work done by force of gravity during first $2$ seconds of the motion is (Take $g = 10 m s^{- 2}$ )

10 J

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20 J

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30 J

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40 J

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Solution

The correct option is D $40 J$
Pulling force $= 3 g - 2 g = g N$
Total mass to be pulled $= 3 + 2 = 5 k g$
Acceleration, $a = \frac{g}{5} = 2 m s^{- 2}$

Displacement of block in first $2$ seconds of its motion,
$S = u t + \frac{1}{2} a t^{2} = 0 + \frac{1}{2} [2] [2]^{2} = 4 m$
Work done by gravitational force,
$W = 30 \times 4 + (- 20 \times 4) = 40 J$

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Consider that the system shown below is released from rest. The work done by force of gravity during first 2 seconds of the motion is (Take g=10 ms−2 )

The correct option is D 40 JPulling force =3g−2g=g N Total mass to be pulled =3+2=5 kg Acceleration, a=g5=2 ms−2 Displacement of block in first 2 seconds of its motion, S=ut+12at2=0+12[2][2]2=4 m Work done by gravitational force, W=30×4+(−20×4)=40 J

Consider that the system shown below is released from rest. The work done by force of gravity during first $2$ seconds of the motion is (Take $g = 10 m s^{- 2}$ )