5 A small box B of weight 400 N is held in equilibrium by two light strings AB and BC . The string BC is fixed at C . The end A of string AB is fixed so that AB is at an angle \(\alpha\) to the vertical where \(\alpha < 60 ^ { \circ }\). String BC is at \(60 ^ { \circ }\) to the vertical. This information is shown in Fig. 5.
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\caption{Fig. 5}
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- Draw a labelled diagram showing all the forces acting on the box.
- In one situation string AB is fixed so that \(\alpha = 30 ^ { \circ }\).
By drawing a triangle of forces, or otherwise, calculate the tension in the string BC and the tension in the string AB .
- Show carefully, but briefly, that the box cannot be in equilibrium if \(\alpha = 60 ^ { \circ }\) and BC remains at \(60 ^ { \circ }\) to the vertical.