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Question: Answered & Verified by Expert
A projectile is projected at $10 \mathrm{~ms}^{-1}$ by making at an angle $60^{\circ}$ to the horizontal. After some time its velocity makes an angle of $30^{\circ}$ to the horizontal. Its speed at this instant is
PhysicsMotion In Two DimensionsKCETKCET 2013
Options:
  • A $\frac{10}{\sqrt{3}}$
  • B $10 \sqrt{3}$
  • C $\frac{5}{\sqrt{3}}$
  • D $5 \sqrt{3}$
Solution:
1240 Upvotes Verified Answer
The correct answer is: $\frac{10}{\sqrt{3}}$
As the velocity makes an angle of $30^{\circ}$ with horizontal, so, the horizontal component of velocity at the instant will be $v \cos 30^{\circ}$.
$\begin{array}{ll}
\Rightarrow & v \cos 30^{\circ}=5 \\
\Rightarrow & v=\frac{5}{\cos 30^{\circ}}=\frac{5}{\sqrt{3} / 2}=\frac{10}{\sqrt{3}}
\end{array}$

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