Question

Case study: A uniform metre rule of mass 100 g is pivoted at its 40 cm mark. A 200 g mass is suspended at its 20 cm mark. To balance the rule horizontally, an unknown mass m is suspended at its 90 cm mark. (The weight of the rule acts at its 50 cm mark.) The value of m is:

A uniform metre rule of weight 80 gf is supported on a knife-edge at its 50 cm mark. A 40 gf weight is suspended from its 20 cm mark. To keep the rule horizontal, a 60 gf weight must be suspended on the other side of the pivot at the:

Case study: A see-saw consists of a uniform wooden plank of length 4 m and mass 20 kg pivoted at its midpoint. A child of mass 30 kg sits at one end of the plank (i.e. 2 m from the pivot). At what distance from the pivot, on the opposite side, must a second child of mass 40 kg sit so that the see-saw remains horizontal? (The weight of the plank acts at the pivot and so produces no moment.)

A uniform metre scale is pivoted at its mid-point 'O'. A weight of 40 gf is suspended at one end of it. Where should a weight of 80 gf be suspended to keep the scale horizontal?