A bike is moving north when the rider applies the brakes. In which direction does the frictional force act between the ground and the bike's wheels?

A.
north

B.
south

C.
upward

D.
downward

What is the frequency of a light wave with a wavelength of 620nm

You are driving directly behind a pickup truck, going at the same speed as the truck. a crate falls from the bed of the truck to the road. (a) will your car hit the crate before the crate hits the road if you neither brake nor swerve? (b) during the fall, is the horizontal speed of the crate more than, less than, or the same as that of the truck?

State the below theories and give the name of the writer of the theory 1. wave theory 2. quantum theory 3. corpuscular theory 4. electromagnetic theory