6. A player hits a ball with a bat. If the action force is the force on the bat against the ball, what is the reaction force? 

A. The force of the gravity

B. The force of the ball on the air

C. The force of the ball on the bat

D. The force of the player’s hand on the bat

7. A girl riding on a skateboard at 3 m/s suddenly hits the curb. The girl will fall ______. 

A. forward at a speed equal to 3 m/s

B. backward at a speed equal to 3 m/s

C. forward with a speed greater than 3 m/s

D. backward with a speed greater than 3 m/s

8. Which of the following statements is not true about power? 

A. Power is a time-based quantity.

B. The standard metric unit of power is the Watt

C. Power refers to how fast work is done upon an object.

D. A force is exerted on an object to move it at a constant speed. The power delivered by this force is the magnitude of the force multiplied by the speed of the object.

9. In a period of 10 seconds, an elevator lifts a weight of 1000 N a distance of 10 m at constant velocity. What is the average power of the elevator over this time?

A. 10000 W

B. 1000 W

C. 100W

D. 10 W

10. A boy carries a heavy bag (20 kilogram) quickly up a flight of stairs. A girl carries the same bag (20 kilogram) slowly up the flight of stairs. Both of them reach the 4th floor of the building. Which conclusion about power and work can you formulate? 

A. The boy had less power than the girl.

B. The boy had more power than the girl.

C. The boy did less work and had less power than the girl.

D. The boy did more work and had more power than the girl.

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