Question

A uniform metre rule balances horizontally on a knife edge at the 25cm mark , when a mass of 30g is hung at the 10cm mark. calculate the mass of the ruler.

Answer 1

Answer:

uniform meter rule = 100cm

let, mass of ruler be= m and  weight of  ruler be = W = mg

now, by principle of moments

=>total clockwise moment =total anti-clockwise moment

=>W x (50-25) = 0.3 x (25-10)

=>mg x (25) = 0.3 x (15)

=>25mg = 4.5

=>m =0.18/g = 0.018 kg = 18 gram = mass of ruler

hope the diagram below helps :)