An object of mass $3 \mathrm{~kg}$ is tied by a string of negligible mass to a ceiling and held such that the string is taut. The object is released suddenly such that the string remains taut. It's acceleration when released is (acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )

• A

  $3.5 \mathrm{~ms}^{-2}$
• Correct answer
  B

  $4.9 \mathrm{~ms}^{-2}$
• C

  $7.5 \mathrm{~ms}^{-2}$
• D

  $6.9 \mathrm{~ms}^{-2}$

Solution

When object is released, net force acting on it is $\mathrm{mg}$ $\sin 30^{\circ}$ as shown, because $\mathrm{T}=\mathrm{mg} \cos 30^{\circ}$ So, $\mathrm{a}=\frac{\mathrm{mg} \sin 30^{\circ}}{\mathrm{m}}=\mathrm{g} \sin 30^{\circ}=4.9 \mathrm{~m} / \mathrm{s}^2$

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