Question

a uniform metre scale balances at 40cm mark when weight of 20g and 40g are suspended at 10 cm and 20cm mark respectively. the mass of the metre scale is
A) 200g
B)60g
C)70g
D)140g​

Answer 1

Given :

Balances at 40 cm mark.

W₁ = 20 g     Suspended at 10 cm

W₂ = 40 g    Suspended at 20 cm

To find :

The mass of the metre scale

Solution :

Moment in clockwise direction = W(50 - 40)

                                                   = 10W

Moment in anti-clockwise direction = 20(40 - 10) + 40(40-20)

                                                           = 20 × 30 + 40 × 20

                                                           = 600 + 800

                                                           = 1400  g cm  

By the law of moment :

Moment in clockwise direction = Moment in anti-clockwise direction

10W =  1400

W = 140g

The mass of the metre scale is 140g.