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Q. A bucket full of water weighs $5 \, kg$ , it is pulled from a well $20 \, m$ deep. There is a small hole in the bucket through which water leaks at a constant rate. If it is observed that for every metre the bucket loses $0.2 \, kg$ mass of water, then the total work done in pulling the bucket up from the well is [ $g=10 \, m \, s^{- 2}$ ]

NTA AbhyasNTA Abhyas 2020Work, Energy and Power

Solution:

The weight of bucket when it has been pulled up a distance $x \, is \, (5-0.2\,x)$
Hence, the required work is
$W=\displaystyle \int _{x = 20}^{x = 0} - \left(5 - 0.2 x\right) \times 10 \times d x$
$=\left[50 x\right]_{x = 0}^{x = 20}-\left[2 \frac{x^{2}}{2}\right]_{x = 0}^{x = 20}$
$W=50\times 20-\left(20\right)^{2}=600 \, J$