Question

This question is worth 20 marks Figure 2 shows a decorator's plank, which is 5 m in length, supported on two trestles. The mass of the plank is 37 kg and the mass of the decorator is 70 kg. In order to paint a stairwell the decorator has to position themselves at point A, as shown on Figure 2. To stop the plank tipping, the decorator's assistant attaches weights to a rope at point B Figure 2 The decorator's plank Long description a. Draw a diagram showing all the forces acting on the plank and the distances from point B that each force acts (4 marks) b. State, in words, two conditions that must be satisfied for the plank to be stationary and stable (2 marks) C. For each of the two conditions you have identified in part (b), using the information contained in your diagram, write an equation that must be satisfied for the bar to remain stationary. Do not include units in your equations (4 marks) d. What is the minimum weight (in newtons) that the assistant must attach to the rope to prevent the plank from tipping? (Hint: think about the reaction forces at the trestle nearest the rope at the point when the plank just begins to tip.) Give your answer to 2 significant figures (6 marks) e. If the rope has a diameter of 22 mm, calculate the stress in the rope when applying the force you calculated in part (d). Give your answer to 2 significant figures (4 marks) The acceleration due to gravity, g, is assumed to be 9.8 m s2

Answer 1

2-5m WA 8 RI b Conditions a point Csaq D ust be equal to zerd (d) 어시B/ F So equa 2 becomes

3 に: 3 stressForce 232.S7 2 N/m2. 743336.87 =