WJEC Physics for AS Level: Revision Workbook

Q18 A uniform public house sign of width 80 cm and mass 3.5 kg is suspended from a metal bar of mass 1.5 kg and length 90 cm by two links, A and B , each of which is 10 cm from the edge of the sign. The metal bar is attached to the wall by a hinge, H . Link A is 15 cm from H . The metal bar is also attached to the wall by a wire which is attached to the bar at B . 30 B T H A ° Ye Olde Black Bull (a) Explain why the tensions in the two links, A and B , are equal and calculate their magnitude. 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(b) Calculate the sum of the clockwise moments, about H , of the forces on the bar. 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(c) By considering moments about H , calculate the tension, T , in the wire, stating which principle for equilibrium you use. 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(d) The hinge, H , also exerts a force on the metal bar. Using a different condition for equilibrium, determine the magnitude and direction of the force exerted by the hinge on the bar. 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