Question

What is the position of centre of gravity of a cylinder?
A. At the centre of the base circle
B. At the centre of top circle
C. Cannot be determined
D. At the mid-point on the axis of cylinder

Answer 1

Hint: Centre of body and centre of gravity will be at the same position for the uniform structures. Centre of gravity can be defined as the balancing point at which the whole weight of the body is concentrated. So, we can balance the whole body if we are holding at that point.

Complete step-by-step answer:
Centre of gravity is the point at which the whole body can be balanced, called a balancing point or it is the point at which the whole weight of the body is concentrated. For a uniform, regular structure the centre of gravity will be at its body centre, that is the middle of the cylinder. For a cylinder, the centre of the body will be at the centre of its axis. So the centre of gravity also will be at the mid-point on the axis of the cylinder. So the correct option is D.

Additional information:
Centre of gravity (CG) is the point at which the distributed weight of a body gets balanced. The balancing point of a solid object is fixed, but that of a flexible body may change accordingly. Distribution of weight at each point a body determines the centre of gravity. It can be calculated using the moments at each point of distribution and total weight. The moments at each point will be equal to the product of the weight and distance of the point from the centre of the body axis. The equation for finding the centre of gravity is,
$CG=\dfrac{{{W}_{1}}{{d}_{1}}+{{W}_{2}}{{d}_{2}}+{{W}_{3}}{{d}_{3}}}{W}$, where ${{W}_{1}}$, ${{W}_{2}}$, and ${{W}_{3}}$ are weights of each point in a body, ${{d}_{1}}$, ${{d}_{2}}$, and ${{d}_{3}}$ are the distances of the points from the centre of the body axis and W is the total weight.

The figure simply tells how a rod can be balanced at a point of the centre of gravity.

Note: In a uniform body, the balancing point will be exactly at the centre of the body. But the centre of gravity of a body with non-uniform mass distribution may not be at its centre. The concept of the centre of gravity is important in studying the stability of a body. A body with a high centre of gravity will be with low stability. Centre of gravity is sometimes referred to as the centre of mass if the acceleration due to gravity is the same for all the points of that body.