An object of mass 5 kg falls from rest through a vertical distance of 20 mand achieves a velocity of 10 m/s. How much work is done by the resistance of the air on the object? `(g=10m//s^2)`

Explanation

Applying work-energy theorem.
work done by all the forces=change in kinetic energy
or `W_(mg) = W_("air") = 1/2 mv^2`
`W_("air") = 1/2 mv^2 - m_(mg) = 1/2 mv^2 - mgh = 1/2 xx 5 xx (10)^2 - (5) xx (10)^2 - (5) xx (10) xx (20) = - 750 J`