Armed with highly sensitive detection equipment, you are in the front of a railroad carthat is accelerating forward. Your friend atthe rear of the car shines green light towardyou. Do you find the light to be red-shifted (low-ered in frequency), blue-shifted (increased infrequency), or neither? Explain. (Hint: Think in terms of the principle of equivalence. What is your accelerating railroad car equivalent to?

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.