The mass of the earth is about 81 times that of the moon. When the spacecraft passes through a certain position between the moon and the earth, the gravity of the moon and the earth is equal. The distance ratio from the position to the center of the moon and the center of the earth is () A. 1：81B. 1：27C. 1：9D. 1：3

The mass of the earth is about 81 times that of the moon. When the spacecraft passes through a certain position between the moon and the earth, the gravity of the moon and the earth is equal. The distance ratio from the position to the center of the moon and the center of the earth is () A. 1：81B. 1：27C. 1：9D. 1：3

Suppose that the distance between the position of the spacecraft and the center of the moon is R1, and the distance between the position of the spacecraft and the center of the earth is R2, there are: GM moon MR12 = GM earth mr22. The mass of the earth is about 81 times that of the moon, and the solution is: r1r2 = 19. So C is correct, a, B, D are wrong, so C is selected

It is known that the mass of the spaceship is M1, the mass of the earth is m2, the mass of the moon is m3, and the distance between the earth and the moon is L. when a spaceship flies from the earth to the moon, it receives the gravitational force of the two spheres in the same direction, the distance between the spaceship and the earth is L

Let the distance between the spaceship and the earth be X,
Then the gravity between the spaceship and the earth is F1 = gm1m2 / X2 (here is the square of x)
The gravity between the spacecraft and the moon is F2 = gm1m3 / (l-x) 2 (the square of (l-x))
F1＝F2
Solve x, (the final expression has a root sign)

How long does it take from the earth to the moon?

The earth is about 380000 kilometers away from the moon. How long does it take? According to Einstein's theory of relativity, the maximum speed is the speed of light, and the minimum speed is 0. For example: if the distance is 1 km, I can use the speed of a bicycle or a car, and the time is different. From this point of view, there are no conditions for you to ask, The time is greater than or equal to 1.27 seconds ＜ if the motion of the object is less than the speed of light ＞