What is meant by a “null point” in the gravitational field of two point masses placed on a straight line?
(a) A point where the gravitational potential is zero
(b) A point where the magnitudes of the gravitational forces due to the two masses on a test mass are equal
(c) A point where the net gravitational field strength is zero
(d) A point where the gravitational potential energy of a test mass is maximum (least negative)