A particle is projected at an angle of $60°$ to the horizontal with a speed of $10 \mathrm{m} {\mathrm{s}}^{-1}$. After some time the direction of its velocity makes an angle of $30°$ to the horizontal. The speed of the particle at this instant is

• A

  $\frac{5}{\sqrt{3}} \mathrm{m} {\mathrm{s}}^{-1}$
• B

  $5\sqrt{3} \mathrm{m} {\mathrm{s}}^{-1}$
• C

  $5 \mathrm{m} {\mathrm{s}}^{-1}$
• Correct answer
  D

  $\frac{10}{\sqrt{3}} \mathrm{m} {\mathrm{s}}^{-1}$

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