Question

A meter stick is supported by a knife-edge at the 50-cm mark. Doug hangs masses of 0.40 and 0.60 kg from the 20-cm and 80-cm marks, respectively. Where should Doug hang a third mass of 0.30 kg to keep the stick balanced?

Answer 1

note 0.60 > 0.40, the third mass 0.30 kg must be on theleft side, assuming x from the left end (0 cm)

Σtorque about the pivot = 0

0.30*(50 - x) + 0.40*(50 - 20) - 0.60*(80 - 50) = 0

x = 30 cm

∴Doug should hang a third mass of 0.30 kg from the 30-cmmark.