On the line of centres between the Earth and the Moon, there is a point where the net gravitational force is zero. Given that the distance between the two is 385,000 km, and that the Earth has a mass 81x that of the Moon, how far is this point from Earth?
Here, we must consider Newton's Law of Universal Gravitation. This states that the gravitational force acting between two bodies is proportional to the masses of each body and inversely proportional to the square of the distance between them, F=Gm1m2/r2 As the Earth is 81 times the mass of the moon, the distance of this point from the moon must be 1/811/2 = 1/9 that of the distance to Earth. This means that we are dealing with a ratio of 1/9 of our distances. We therefore take 385000 * 9/(9+1) to find the distance, which is equal to 346,500 km, or 347,000 km to 3 significant figures.
PR
Related Physics A Level answers
All answers ▸A small ball of mass 150 g is placed at a height of 20cm above the ground on an incline of 35°. It is released and allowed to roll down the slope; what will be the ball's speed when it reaches the ground? Assume friction and air resistance can be ignored.
Derive an expression for the time taken, (t) for a test mass to fall to the ground from a height (h) in a uniform gravitational field (g = 9.81 ms^-2)
What does the photoelectric effect demonstrate?
Which are the types of carrier movements and how are they activated