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 uch mass hsould be removed from teh balloon so that it may rise with a constant velocity v?

Explanation

To solve the problem, we need to analyze the forces acting on the balloon when it is falling and when it is rising.

### Step-by-Step Solution:

1. **Identify the Forces When the Balloon is Falling:**
- When the balloon is falling with a constant velocity \( v \), the net force acting on it is zero. The forces acting on the balloon are:
- Weight of the balloon \( W = Mg \) acting downwards.
- Buoyant force \( B \) acting upwards.
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