The force of buoyancy exerted by the atmosphere
Question:

The force of buoyancy exerted by the atmosphere on a balloon is B in the upward direction and remains constant. The force of air resistance on the balloon acts opposite to the direction of velocity and is proportional to it. The balloon carries a mass $M$ and is found to fall down near the earth’s surface with a constant velocity v. How much mass should be removed from the balloon so that it may rise with a constant velocity v?

Solution: