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Consider a drop of rain water having mass 1 g falling from a height of 1 km. It hits the ground with a speed of 50 m/s. Take 'g' constant with a value 10 m/s2. The work done by the (i) gravitational force and the (ii) resistive force of air is
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- (i) 1.25 J (ii) –8.25 J
- (i) 100 J (ii) 8.75 J
- (i) 10 J (ii) – 8.75 J
- (i) – 10 J (ii) –8.25 J
Correct Option: C
From work-energy theorem,
Wg + Wa = ∆K.E
| or, mgh + Wa = | mv2 - 0 | |
| 2 |
| = 10–3 × 10 × 103 + Wa = | × 10–3 × (50)2 | |
| 2 |
⇒ Wa = –8.75 J which is the work done due to air resistance
Work done due to gravity = mgh = 10–3 × 10 × 103 = 10 J
