An empty plastic box of mass m is found to accelerate up at the rate of g/6 when placed deep inside water. How much sand should be put inside the box so that it may accelerate down at the rate of g/6?
Given:
Mass = m
Case I:
When it accelerates upward with acceleration = 
Let B be the buoyant force.
Thus,
Case II:
When it accelerates downward with acceleration =
after addition of sand of mass 
Thus,
∴ 
1