A balloon with mass ‘m’ is descending down with an acceleration ‘a’ (where a < g). How much mass should be removed from it so that it starts moving up with an acceleration ‘a’?
Answer & explanation
Correct answer: option 1
Let up thrust of air be Fb then for downward motion mg – Fb = ma
Let's assume that mass m' be removed from the balloon
So when it start moving upward
Fb - (m - m') g = (m - m')a
m' = \(\frac{2ma}{g+a}\)