In order to solve the problem, you will need an expression for the added mass for a body of a certain shape.
Mathematically, finding this added mass is the most challenging part of the solution. The next hint will be on how to calculate this added mass.
Please submit the solution to this problem via e-mail to physcs.cup@gmail.com. The Hint No 4 will be published on 26th November, 13:00 GMT.