It will be 3 wavelengths because 1 cycle = 1 wavelength.
Air, because it is the least dense material listed, meaning that light can travel through it quicker because there are less particles for it to collide with which would cause it to slow down as it loses energy with each collision
The first one is C. Hope this helps!! If you need anymore help just message me and I will try to get back to you quickly and help in any way i can!
The work done against the gravitational force goes into an important form of stored energy that we will explore in this section. ... If the object is lifted straight up at constant speed, then the force needed to lift it is equal to its weight mg. The work done on the mass is then W = Fd = mgh.