"Find the velocity of a falling body at t=5 seconds
Air resistance is proportional to the velocity of the body.
weight of the body=50kg
Height = 100m
Initial velocity = 5m/sec
Limiting velocity = 65/sec"

I've assumed earth gravity above. However, if you integrate again to find the height after 5 seconds you get a negative height, so perhaps this isn't on earth! Also, air resistance is more normally taken to be proportional to velocity squared (though this means there is no nice closed form solution for velocity as a function of time - it has to be calculated numerically).