Julie drives 90 mi to Grandmother's house. On the way to Grandmother's, Julie drives half the distance at 20 mph and half the distance at 70 mph . On her return trip, she drives half the time at 20 mph and half the time at 70 mph . Part B:

How long does the return trip take?
I would really appreciate a step by step to learn this portion. I dont think I quite grasp the idea of this part

Explain why the aperture of the spherical mirror should be small compared to the radius of curvature of the mirror.

Unpolarized light falls on two polarizer sheets whose transmission axes are at right angles. a third polarizer is placed between the first two so that its axis makes a 52-degree angle with the axis of the first polarizer. a) what fraction of the incident light intensity is transmitted through the first polaroid? b) what fraction of the incident light intensity is transmitted through the second polaroid? c) what is the angle of polarization of the light that enters the third polaroid? d) what fraction of the incident light intensity is transmitted through the third polaroid. e) what happens if the middle polaroid is removed?

When you push downward on a book at rest on a table, you feel an upward force. does this force depend on friction? defend your answer.