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’ ?

• A

  $\frac{2\mathrm{ma}}{\mathrm{g}+\mathrm{a}}$

• B

  $\frac{2\mathrm{ma}}{\mathrm{g}-\mathrm{a}}$

• C

  $\frac{\mathrm{ma}}{\mathrm{g}+\mathrm{a}}$

• D

  $\frac{\mathrm{ma}}{\mathrm{g}-\mathrm{a}}$