NEET | 2017GravitationHard

Question

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 :-

Options

A.

(i) 1.25 J     (ii) – 8.25 J

B.

(i) 100 J     (ii) 8.75

C.

(i) 10 J      (ii) – 8.75 J

D.

(i) – -10 J      (ii) –- 8.25 J

Solution

Work done by the gravity (Wg) = mgh
= 10-3 × 10 × 10-3 = 10 J
By work–energy theorem = Wg + Wres = ∆KE
10 + Wres = 12×10-3 × (50)2
Wres =  - 8.75 J

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