Newton's Law of Gravitation
(1) Centre of gravity (C.G) of a body is the point at which the weight of the body acts (2) Centre of mass coincides with the centre of gravity if the earth is assumed to have infinitely large radius.
(3) 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.
(4) 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?
Show answer and solution
Answer: (a)
- (1) True: C.G. is the point where the total weight of the body acts.
- (2) True: for an earth of infinite radius is uniform over the body, and then C.M. and C.G. coincide.
- (3) False: treating the whole mass as concentrated at one point is exact only for spherically symmetric bodies.
- (4) False: radius of gyration is defined by , not as the perpendicular distance of the C.G. from the axis.
- So the correct pair is (1) and (2), option (b).