1. The centre of gravity is that point at which the sum of the gravitational forces due to all individual masses comprising the system appears to act. The net torque about the centre of gravity due to the gravitational forces on the masses in the system is zero

2.  A seesaw consisting of a uniform board of mass M and length l supports a father and daughter with masses m f and m d respectively. The support is under the centre of gravity, and the father and daughter are seated a distance of d and l /2 from it.

3.  n + Mg + m f g + m d g = 0 ) Determine the magnitude of the upward force n

4.  A uniform 8 m long horizontal beam with a weight of 200 N is attached to a wall by a pin. Its far end is supported by a cable making a 53° angle with the beam. A 600 N person stands 2 m from the wall. Determine the tension in the cable and the magnitude and direction of the wall’s force on the beam.

5. We start by identifying all the forces acting on the beam: