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  4. A block of mass 2 kg is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force F=40 N. The kinetic energy of the particle increase 40 J in a given interval of time. Then: (g=10 m / s 2)

Q. A block of mass $2\, kg$ is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force $F=40\, N$. The kinetic energy of the particle increase $40\, J$ in a given interval of time. Then: $\left(g=10\, m / s ^{2}\right)$Physics Question Image

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Solution:

image
Free body diagram of block is as shown in figure.
From work-energy theorem
$W_{\text {net }}=\Delta KE \text { or }(40-20) s=40$
or $s=2\, m$
Work done by gravity is $-20 \times 2=-40\, J$
and work done by tension is $40 \times 2=80\, J$

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