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NEET 2017
Exam
NEET
Year
2017
Subject
Physics
Chapter
Work, Power and Energy

NEET 2017 · Physics · Work, Power and Energy

Consider a drop of rain water having mass 1g falling from a height...

Consider a drop of rain water having mass 1g1g falling from a height of 1km1km. It hits the ground with a speed of 50ms−150m{s}^{- 1}. Take gg constant with a value 10ms−210m{s}^{- 2}. The work done by the (i) gravitational force and the (ii) resistive force of air is

Options

  1. A{(i)−10J(ii)−8.25J\begin{cases}\left(i\right) - 10J & \left(ii\right) - 8.25J\end{cases}
  2. B{(i)1.25J(ii)−8.25J\begin{cases}\left(i\right)1.25J & \left(ii\right) - 8.25J\end{cases}
  3. C{(i)100J(ii)8.75J\begin{cases}\left(i\right)100J & \left(ii\right)8.75J\end{cases}
  4. D{(i)10J(ii)−8.75J\begin{cases}\left(i\right)10J & \left(ii\right) - 8.75J\end{cases}

Correct answer

D. {(i)10J(ii)−8.75J\begin{cases}\left(i\right)10J & \left(ii\right) - 8.75J\end{cases}

Step-by-step solution

By Work-Energy Theorem

Wg+Wa=Kf−Ki{W}_{g} + {W}_{a} = {K}_{f} - {K}_{i}

mgh+Wa=12mv2−0mgh + {W}_{a} = \dfrac{1}{2}m{v}^{2} - 0

10−3×10×103+wa=12×10−3×(50)2{10}^{- 3} \times 10 \times {10}^{3} + {w}_{a} = \dfrac{1}{2} \times {10}^{- 3} \times {\left(50\right)}^{2}

Wa=−8.75J{W}_{a} = - 8.75J

work done due to gravity =mgh= \text{mgh}

=10−3×10×103= {10}^{- 3} \times 10 \times {10}^{3}

=10J= 10\text{J}
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