A box when dropped from a certain height reaches the ground with a speed $v$. When it skides from rest from the same height down a rough inclined plane inclined at in angle $45^{\circ}$ to the horizontal, it reaches the ground with a speed $v / 3 .$ The coefficient of sliding friction between the box and the plane is (acceleration due to gravity is $10 \mathrm{~ms}^{-2}$ )

• Correct answer
  A

  $\frac{8}{9}$
• B

  $\frac{1}{9}$
• C

  $\frac{2}{3}$
• D

  $\frac{1}{3}$

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