Question

The diagram below shows 2 half-metre rules that are marked off at 5cm intervals and IDENTICAL metal discs are placed on the rules as shown. In each case state whether the rules will turn anticlockwise, clockwise or remain in the horizontal position. SHOW YOUR WORKING.

Answer 1

Explanation:

Let the weight of the half metre rule be x gf and it acts at the 25 cm mark (centre of gravity).

Now,

Acticlockwise moment = x×4

Clockwise moment = 20×21

In equilibrium,

Anticlockwise moment = Clockwise moment

4x=20×21

x=105 gf.

Thus, the weight of the metre rule is 105gf.

We know, one gf is the force acting on the body of mass 1 grams, thus mass of the body is 105grams.