Which type of force is used by your legs to pedal a bicycle?

gravity
friction
strong push
weak pull

What is a carrier wave and how does it affect what you hear on the radio

Light traveling in water, nwater = 1.33, strikes a plastic block at an angle of incidence of 51.4°; part of the beam is reflected and part is refracted. if the index of refraction of the plastic is 2.0, what is the angle made by the reflected and refracted beams?

What sort of waves exhibit the doppler effect?