Question

If you place pivot at centre of a meter rule, weight has no
A. Property
B. Concern
C. Turning effect
D. Magnitude

Answer 1

This problem is based on the principle of moment of force or turning effect of force. According to the principle of moment of force the sum of clockwise moments is equal to the sum of anticlockwise moments.

Complete answer:

The centre of gravity is the point about which the algebraic sum of moments of weights of all the particles constituting the body is zero. The entire weight of the body can be considered to act at this point, however the body is placed. The centre of gravity for the metre rule will lie at the midpoint of the metre rule that is at the $50\,cm$ mark for the $100\,cm$ rule.

The weight of an object is concentrated at the centre of gravity and hence a pivot at the centre of the metre scale. Therefore the scale does not turn around that is it balance on the fulcrum if the fulcrum is placed at the midpoint of the metre rule

Hence, the correct option is C.

Additional information: Position of centre of gravity for some regular object are as follows:

Object	Position of centre of gravity
Circular disc	Geometric centre
Solid or hollow sphere	Geometric centre
Solid or hollow cylinder	Mid point on the axis of cylinder
Solid cone	At a height $\dfrac{h}{4}$ from the base, on its axis
Hollow cone	At a height $\dfrac{h}{3}$ from the base, on its axis
Circular ring	Centre of ring
Triangular lamina	The point of intersection of medians
Parallelogram	The point of intersection of the diagonals

Note: The position of the centre of gravity of the body of the given mass depends on the shape of the body. It changes if the body is deformed. It is necessary that the centre of gravity always be within the material of the body.