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Physics · PYQ NEET UG 2017
हिन्दीConsider a drop of rain water having mass \( 1\text{ g} \) falling from a height of \( 1\text{ km} \). It hits the ground with a speed of \( 50\text{ m/s} \). Take ' \( g \) ' constant with a value \( 10\text{ m/s}^2 \). The work done by the (i) gravitational force and the (ii) resistive force of air is:
Correct answer · Option 4
(i) \( 10\text{ J}\quad \) (ii) \( -8.75\text{ J} \)
Explanation
Work by gravity \( W_g = mgh = 10^{-3} \times 10 \times 1000 = 10\text{ J} \). By work-energy theorem, \( W_g + W_{\text{air}} = \Delta K = \frac{1}{2}mv^2 - 0 = \frac{1}{2} \times 10^{-3} \times (50)^2 = 1.25\text{ J} \). Thus, \( W_{\text{air}} = 1.25 - 10 = -8.75\text{ J} \).
