A body of mass $0.05 \mathrm{~kg}$ is observed to fall with an acceleration of $9.5 \mathrm{~ms}^{-2}$. The opposing force of air on the body is $\left(g=9.8 \mathrm{~ms}^{-2}\right)$

• Correct answer
  A

  $0.015 \mathrm{~N}$
• B

  $0.15 \mathrm{~N}$
• C

  $0.030 \mathrm{~N}$
• D

  zero

Solution

From, Newton's laws of motion,

or $\begin{aligned} \mathrm{mg}-\mathrm{F}_{\mathrm{air}} &=\mathrm{ma} \\ \mathrm{F}_{\mathrm{air}} &=\mathrm{m}(\mathrm{g}-\mathrm{a}) \\ &=0.05(9.8-9.5) \\ &=0.015 \mathrm{~N} \end{aligned}$

Hence, the correct answer is option: 'A'.