Question 88 of 210

A block of $\sqrt{3}kg$ is attached to a string whose other end is attached to the wall. An unknown force $F$ is applied so that the string makes an angle of $30^{\circ}$ with the wall. The tension $T$ is : (Given g $=10m{s}^{–2}$)

A$20N$B$25N$C$10N$D$15N$

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Answer: (A) $20N$

From geometry, $\theta =30^{\circ}$.
For equilibrium,
$T\cos \theta =mg$
$\Rightarrow T=\dfrac{mg}{\cos 30^{\circ}} \Rightarrow T=\dfrac{\sqrt{3}\times 10}{\dfrac{\sqrt{3}}{2}}$
$\Rightarrow T=20N$