## Question

# 1) How much work does a supermarket checkout attendant do on a can of soup he pushes 0.810 m horizontally with a force of 5.60

1) How much work does a supermarket checkout attendant do on a can of soup he pushes 0.810 m horizontally with a force of 5.60 N? Express your answer in joules and kilocalories. (For each answer, enter a number.)

work in joules =......J

work in kilocalories = .......kcal

2) How much work (in J) is done by the boy pulling his sister35m in a wagon as shown in the figure below?

A boy pulling a wagon with a child sitting in the cart along a horizontal surface. The boy is shown pulling the handle of the wagon at an angle of 30above the horizontal. Along the length of the handle, a diagonal arrow labeled**F**extends from the wagon to the boy. A horizontal arrow labeled*d*extends from the wagon to the boy.

Assume no friction acts on the wagon. (Assume*d*=35mand*F*=51N. Enter a number.)

*W*=....J

3) Suppose a car travels 108 km at a speed of 35.0 m/s, and uses 1.80 gallons of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (The energy content of gasoline is 1.30 10^{8} J per gallon.)

(a) What is the force (in N) exerted to keep the car moving at constant speed? (Enter a number.) = ....N

(b) If the required force is 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.) = .....gallons

4) Using energy considerations, calculate the average force (in N) a 66.0 kg sprinter exerts backward on the track to accelerate from 2.00 to 6.50 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him. (Enter a number.) = .....N

5) A car's bumper is designed to withstand a 5.76 km/h (1.6 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 0.165 m while bringing a 890 kg car to rest from an initial speed of 1.6 m/s. (Enter a number.) = ......N

6) (a) How much gravitational potential energy (in J) (relative to the ground on which it is built) is stored in an Egyptian pyramid, given its mass is about 8 10^{9} kg and its center of mass is 34.0 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 10^{7} J)? (Enter your answer as a ratio to the number 1. Enter a number.) =..... :1

7) A 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 J) relative to the generators of a lake of volume 47.0 km^{3} (mass = 4.70 10^{13} kg), given that the lake has an average height of 39.0 m above the generators? = .....J

(b) Compare this with the energy stored in a 9-megaton fusion bomb.

*E*_{lake}/*E*_{bomb} = .......

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