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  1. 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’?​
    1. 2ma
      g + a
    2. 2ma
      g - a
    3. ma
      g + a
    4. ma
      g - a
Correct Option: A

Let upthrust of air be Fa then
For downward motion of balloon
Fa = mg – ma
mg – Fa = ma
For upward motion
Fa – (m – ∆m)g = (m – ∆m)a

Therefore ∆m =
2ma
g + a



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