The maximun value of the applied force \(F\) such that the block as shown in the arrangement does not move…

The maximun value of the applied force \(F\) such that the block as shown in the arrangement does not move is (Acceleration due to gravity, \(g=10 \mathrm{~ms}^{-2}\) )
  1. \(20 \mathrm{~N}\)
  2. \(15 \mathrm{~N}\)
  3. \(25 \mathrm{~N}\)
  4. \(10 \mathrm{~N}\)

Solution

Applied force on the block on a horizontal surface, as shown in the figure, we have
As we know that, force of friction, \(f=\mu R\) From the diagram, $\begin{aligned} & f=\mu\left(W+F \sin 60^{\circ}\right) \\ & F \cos 60^{\circ}=\frac{1}{2 \sqrt{3}}\left(10 \sqrt{3}+F \sin 60^{\circ}\right) \\ & \Rightarrow F \times \frac{1}{2}=\frac{1}{2 \sqrt{3}}\left(10 \sqrt{3}+F \times \frac{\sqrt{3}}{2}\right) \quad\left\{\begin{array}{l} \cos 60^{\circ}=\frac{1}{2} \\ \sin 60^{\circ}=\frac{\sqrt{3}}{2} \end{array}\right\} \\ & \Rightarrow \frac{F}{2}=\frac{1}{2 \sqrt{3}} \times \sqrt{3}\left(10+\frac{F}{2}\right) \\ & \Rightarrow \frac{F}{2}=\frac{1}{2} \left(10+\frac{F}{2}\right) \Rightarrow F=\frac{20+F}{2} \\ & \Rightarrow 2 F=20+F \Rightarrow F=20 \\ & \therefore \quad F=20 \mathrm{~N} \\ \end{aligned}$

Asked in: AP EAMCET 2019 (20 Apr Shift 1)

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