7.
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{2def617f-3c25-4458-8500-8e20ba7c1e53-5_355_682_237_550}
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\caption{Fig. 3}
\end{figure}
Figure 3 shows a block of mass 25 kg held in equilibrium on a plane inclined at an angle of \(35 ^ { \circ }\) to the horizontal by means of a string which is at an angle of \(15 ^ { \circ }\) to the line of greatest slope of the plane.
In an initial model of the situation, the plane is assumed to be smooth. Giving your answers correct to 3 significant figures,
- show that the tension in the string is 145 N ,
- find the magnitude of the reaction between the plane and the block.
In a more refined model, the plane is assumed to be rough.
Given that the tension in the string can be increased to 200 N before the block begins to move up the slope, - find, correct to 3 significant figures, the magnitude of the frictional force and state the direction in which it acts.
(4 marks) - Without performing any further calculations, state whether the reaction calculated in part (b) will increase, decrease or remain the same in the refined model. Give a reason for your answer.