Physics
posted by Abubakar .
A uniform meter rule of mass 100g balance at a 40cm mark when a mass x is placed at the 10cm mark.What is x?

x is 30 cm from the fulcrum, and the center of mass of the ruler is 10 cm on the other side of it (in the middle of the ruler). The two moments balance. Therefore
x*30 = 100*10
x = 33.3 g 
X is 30 cm from the pivot, which is at 40cm. The centre of mass is at 50 cm, so the pivot is 10 cm from the centre of mass. Therefore,
f x d(from pivot)= f x d(from c. of m.)
x*30=100*10
x=33.3g
Be careful to keep units correct, and JIHAD