A body is moving with a uniform speed of $20 \mathrm{~ms}^{-1}$ on a horizontal circle. The change in velocity of the body in half revolution is

• A

  $20 \mathrm{~ms}^{-1}$
• B

  $10 \mathrm{~ms}^{-1}$
• Correct answer
  C

  $40 \mathrm{~ms}^{-1}$
• D

  $\frac{20}{\sqrt{2}} \mathrm{~ms}^{-1}$

Solution

Speed of body, $v=20 \mathrm{~m} / \mathrm{s}$ Change in velocity in half revolution
$\begin{aligned} & \Delta v=\vec{v}_2-\vec{v}_1=-v \hat{j}-v \hat{j}=-2 v \hat{j} \\ & |\Delta v|=2 v=2 \times 20=40 \mathrm{~m} / \mathrm{s}\end{aligned}$

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