Question

a uniform half metal rod, A,B is balanced horizontally on a knife edge place 20m from a and with the mass of 35g. what is the mass if the distance from the mass to the pivot 5cm?

Answer 1

If rule is uniform, its center of mass is 25cm from A, 5 cm from the fulcrum.

20 cm x 22.5 g = 5 cm x M, where M is the mass of the rule, 90 g. Note: Some purists may insist on force balance, but as long as there is some gravity and it is constant across the width of the beam, balance beam scales compare masses.

Force on fulcrum is total mass times gravity, (0.0225 kg + 0.090 kg) x 10 N/kg = 1.125 N