The source size is defined to give geometric penumbra width, explain what else contributes to the penumbra width? explain why width of d80-20 is used to characterise penumbra width? would the d80-20 be wider or narrower at high energy and why?

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?