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NEET2014PhysicsLaws of MotionActual

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

  1. A2 m a g + a
  2. B2 m a g - a
  3. Cm a g + a
  4. Dm a g - a

Correct answer

A. 2 m a g + a

Step-by-step solution

Let the upward force be F . When balloon descending down, then m g - F = m a …(i) Let the mass removed be m ' . When balloon ascending upward, then F - m - m ' g = m - m ' a from (i) F - m g + m ' g = m a - m ' a m g - m a - m g + m ' g = m a - m ' a m ' g + a = 2 m a m ' = 2 m a g + a

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