Which of the following best describes why astronauts have to wear gravity boots when they are on the moon but not when they are on the Earth?
A)The moon's gravity is stronger than Earth's gravity.

B)The moon's surface is denser than the Earth's surface.

C)The Earth's gravity pulls them down to the Earth's surface.

D The Earth's surface is magnetic, but the moon's surface is not

When a charged balloon sticks to a wall, the downward gravitational force is balanced by an upward static friction force. the normal force is provided by the electrical attraction between the charged balloon and the equal but oppositely charged polarization induced in the wall's molecules. if the mass of a balloon is 1.2 g, its coefficient of static friction with the wall is 0.71, and the average distance between the opposite charges is 0.80 mm, what minimum amount of charge must be placed on the balloon in order for it to stick to the wall? express your answer to two significant figures and include appropriate units.