A bullet of mass $\mathrm{10\; g}$ moving horizontally with a velocity of $400 \mathrm{m }{\mathrm{s}}^{-1}$ strikes a wooden block of mass $\mathrm{2\; kg}$ which is suspended by a light inextensible string of length $\mathrm{5\; m.}$ As a result, the centre of gravity of the block is found to rise a vertical distance of $\mathrm{10\; cm.}$ The speed of the bullet after it emerges out horizontally from the block will be

• A

  $100 \mathrm{m}{\mathrm{ s}}^{-1}$
• B

  $80 \mathrm{m}{\mathrm{ s}}^{-1}$
• Correct answer
  C

  $120 \mathrm{m}{\mathrm{ s}}^{-1}$
• D

  $160 \mathrm{m}{\mathrm{ s}}^{-1}$

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