Q. Consider a drop of rain water having mass 1g 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 $m/s^2$. The work done by the (i) gravitational force and the (ii) resistive force of air is :
A) (i) -10 J (ii) -8.25 J
B) (i) 1.25 J (ii) -8.25 J
C) (i) 100 J (ii) 8.75 J
D) (i) 10 J (ii) -8.75 J
Explanation
[Solution] $W_g = mgh = 10$ J; KE = $\frac{1}{2}(0.001)(2500) = 1.25$ J; $W_{air} = 1.25 - 10 = -8.75$ J. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.