Q. (a) Centre of gravity (C.G.) of a body is the point at which the weight of the body acts (b) Centre of mass coincides with the centre of gravity if the earth is assumed to have infinitely large radius (c) 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. (d) The radius of gyration of any body rotating about an axis is the length of the perpendicular dropped from the C.G. of the body to the axis Which one of the following pairs of statements is correct?
A) (d) and (a)
B) (a) and (b)
C) (b) and (c)
D) (c) and (d)
Explanation
[Solution from source] The weight of a body acts at its centre of gravity, and if g is uniform over the body (earth of infinite radius) the centre of gravity coincides with the centre of mass, so the first two statements are correct. The gravitational field of a body at an external point can be found by concentrating its mass at one point only for spherically symmetric bodies, and the radius of gyration is defined by I = Mk², not as the distance from the C.G. to the axis. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.