I am stuck on question 3, 5, 6, and 7 . Thank you!

Suppose a car travels 108 km at a speed of 20.0 m/'s, and uses 2.10 gallons of gasoline. Only 30% of the gasollne goes lnto useful work by the force that keeps the car moving at constant speed despite friction. (The energy content of gasoline is 1.30 x 108] per gallon.) (a) What is the..f.orce (ln N) exerted to keep the car moving at constant speed? (Enter a number.) -: (b) If the required force l5 directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s? (Enter a number.) 3:: gal... A car's bumper is designed to withstand a 4.32 km/h (1.2 m/s) collision with an immovable object without damage to the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force (in N) on a bumper that collapses 0.195 m while bringing a 830 kg car to rest from an initial speed of 1.2 m/s. (Enter a number.) N(a) How much gravitational potential energy (in ]) (relative to the ground on which it is built) is stored in an Egyptian pyramid, given its mass is about 4 x 10 kg and its center of mass is 21.0 m above the surrounding ground? (Enter a number.) J (b) What is the ratio of this energy to the daily food intake of a person (1.2 x 10' ])? (Enter your answer as a ratio to the number 1. Enter a number.) :1A hydroelectric power facility converts the gravitational potential energy of water behind a dam to electric energy. (For each answer, enter a number.) (a) What is the gravitational potential energy (in ]) relative to the generators of a lake of volume 20.0 km (mass = 2.00 x 1015 kg), given that the lake has an average height of 31.0 m above the generators? (b) Compare this with the energy stored in a 9-megaton fusion bomb. Elake Ebomb =