Hi :) I’m self-studying for my A Level mechanics 2 exam (it’s in 4 days :S) and there’s a problem in my book that I just can’t solve. Any help would be really appreciated. :) 1. The problem statement, all variables and given/known data Find the sum of the moments about the point P of the forces shown in the diagram: 2. Relevant equations Moment about a point = Force x Perpendicular distance of the force from the point 3. The attempt at a solution From the way the problem diagram is shown in my book, it seems as though APB is a rigid triangular frame. Since we’re finding the sum of the moments about the point P, we won’t be considering the green 2N force and the blue 1N force because they both act along P. We won’t be considering the 5N force either because it doesn’t have any effect on the moments about P. Moment of the blue 2N force about P = 2N x PB = 2N x 5m = 10 Nm anticlockwise Applying the sine rule: (AP / sin 18 degrees) = (PB / sin 40 degrees) Or, AP = sin 18 degrees x (5m / sin 40 degrees) Hence, AP = 2.4037m Moment of the 3N force about P = 3N x 2.4037m = 7.2111 Nm clockwise Hence, moments about P = 10 Nm – 7.2111Nm = 2.7889Nm anticlockwise = 2.79 Nm anticlockwise My book’s answer is 2.07 Nm anticlockwise. Could someone please tell me where I’m going wrong?