WJEC Physics for AS Level: Revision Workbook

2. A simple bridge over a stream consists of a uniform plank of mass 44 kg and length 2.4 m, hinged to a vertical post and kept horizontal by a rope joining the end of the plank to the post. string post hinge rope plank 35° pulley 0.20 kg 0.42 kg pointer ruler 1.0 kg truck 5.0 kg block _ b b ` b b a 2.4 m (a) (i) Calculate the moment about the hinge of the plank’s weight. 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(ii) Hence show that the tension in the rope is approximately 400 N. 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(iii) Calculate the horizontal component of the force that the hinge exerts on the plank, explaining your reasoning. 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(b) The makers of the rope state that the maximum safe tension is 1500 N. Evaluate whether it would be safe for a student of mass 68 kg to walk across the plank, starting at the post. 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