STANDARD Physics Work-Energy Theorem MCQ Question
A raindrop of mass 1 g falling from a height of 1 km hits the ground with a speed of 50 m s⁻¹. If the resistive force is proportional to the speed of the drop, then the work done by the resistive force is (Take g = 10 m s⁻²)
10 J
−10 J
8.75 J
−8.75 J
Correct Answer
Detailed Explanation
The change in kinetic energy of the drop is ΔK = 1/2 m v² - 0 = 1/2 × 10⁻³ × 50 × 50 = 1.25 J. The work done by the gravitational force is Wg = mgh = 10⁻³ × 10 × 10³ = 10 J. According to the work-energy theorem, K = Wg + Wr, where Wr is the work done by the resistive force. Thus, Wr = ΔK − Wg = 1.25 J − 10 J = −8.75 J.
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