Question

A uniform bar RS weighs 100 g and is 80 cm long. From the end R, two masses 50 g and 100 g are hung from the bar at a distance of 10 cm and 60 cm respectively. If the bar is to remain horizontal when balanced on a knife-edge, its position is ____________.

Options

• 42 cm from S

• 38 cm from R

• 38 cm from G

• 42 cm from R

Answer 1

A uniform bar RS weighs 100 g and is 80 cm long. From the end R, two masses 50 g and 100 g are hung from the bar at a distance of 10 cm and 60 cm respectively. If the bar is to remain horizontal when balanced on a knife-edge, its position is 42 cm from R.

Explanation:

Let the knife - edge be balanced at x cm from point R. For equilibrium, considering moments about point R,

W₁ × RA + W x RG + W₂ x RB = (W₁ +W+ W₂) × x 

50 × 10 + 100 × 40 + 100 × 60 = (50 + 100+ 100) x

`Rightarrow "x" = (500 xx 4000 xx 6000)/250 = 42  "cm"`