Laws Of Motion Question 276

Question: 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’?

Options:

A) $ \frac{2ma}{g+a} $

B) $ \frac{2ma}{g-a} $

C) $ \frac{ma}{g+a} $

D) $ \frac{ma}{g-a} $

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Answer:

Correct Answer: A

Solution:

[a] Let up thrust of air be

$ ~F _{a} $ then For downward motion of balloon $ F _{a}=mg-ma $

$ mg-F _{a}=ma $

For upward motion $ F _{a}-( m-\Delta m )g=( m-\Delta m )a $

Therefore $ \Delta m=\frac{2ma}{g+a} $



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