Question

$\left(a\right)$ Centre of gravity $(C.G.)$ of a body is the point at which the weight of the body acts.
$\left(b\right)$ Centre of mass coincides with the centre of gravity if the earth is assumed to have infinitely large radius.
$\left(c\right)$ To evaluate the gravitational field intensity due to any body at an external point, the entire mass of the body can be considered to be concentrated at its $(C.G.)$
$\left(d\right)$ The radius of gyration of any body rotating about an axis is the length of the perpendicular distance from the $(C.G.)$ of the body to the axis.

Which one of the following pairs of statements is correct?

• A. (b) and (c)
• B. (c) and (d)
• C. (a) and (c)
• D. (a) and (b)

Answer 1

The correct option is C (a) and (c)

$\left(a\right)$ Center of gravity is the point where weight acts.
$\left(b\right)$ Center of mass coincides with center of gravity in the case where mass density is uniform.
$\left(c\right)$ Gravitational field at any extreme point can be calculated, assuming it to be a point mass.
$\left(d\right)$ We can define the radius of gyration as the imaginary distance from the centroid at which the area of cross-section is imagined to be focused at a point, in order to obtain the same moment of inertia. Thus, the given statement regarding radius of gyration is incomplete.

Hence, $\left(A\right)$ is the correct answer.