A body of mass 1 kg falls from rest through a distance of 200 m and acquires a speed of 50 m/s. Work done against friction of air is (Take `g = 10 m//s^2)` 

Options

A. 700 J
B. 1250 J
C. 750 J
D. 1960 J

Answer

C

Explanation

PE lost = `mgh = 1 xx 10 xx 200 = 2000 J`
KE gained = `1/2 mv^2 = 1/2 xx 1 xx (50)^2 = 1250 J`
Work done against friction of air = `2000 J - 1250 J = 750 J` .