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Power

Explore various scenarios to comprehend power calculation in physics. From lifting weights to rowing and carrying bags, we demonstrate how to calculate power using work done over time. Examples include lifting books, carrying cousins, and kicking soccer balls, illustrating both positive and negative power values. We discuss the relationships between force, distance, and time, helping you grasp these concepts effectively. Whether you're studying for a quiz or just curious about physics, this guide simplifies power calculations in daily activities.

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Power

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  1. Power “Quiz” Tomorrow

  2. You lift a 3 N book 2 m for 3 seconds. How much power did you use? • 3 N x 2 m = • 6 J • 6 J/ 3 s = • 2 W

  3. You carry a 3 N book 5 m for 60 seconds. How much power did you use? • 0 J • 0 J/ 60 s= • 0 W

  4. You lift two 4 N books 2 m/s. How much power did you use? • (4N + 4N) x 2m = • 16 J • 16 J/ 1 s= • 16 W

  5. A crew member uses 800 N to row an oar’s handle 0.5 m for 1 minute. How much power did the crew member use? • 800 N x 0.5 m = • 400 J • 400 J/60 s = • 6.7 W

  6. You lift your 50 N cousin 1.5 m for 1.25 minutes. How much power do you use? 50 N x 1.5 m = 75 J 75 J/75 s = 1 W

  7. You went shopping and filled two bags. You need to carry both bags up the stairs. Would you use more power if you carried one bag at a time or both bags at the same time? • The work would be the same, but the power would be greater with 2 bags at once, since it would take less time.

  8. A giraffe lifts his 3 N head 2 m in 1 minute. How much power did he use to reach the food on the top branch? • 3 N x 2 m = • 6 J • 6J/60 s = • 0.1 W

  9. A soccer player kicks a 1 N ball 8 m to the goal in the last 2 seconds of the game. How much power would the goalie have to use in order to stop the ball? • 1 N x -8 m = • -8 J • -8 J/2 s= • -4 W • Negative because the goalie is working opposite the kicker.

  10. A student lifts three 3 N books 0.5 m in 1 second. How much power did the student use? • (3 x 3 N) x 0.5 m = • 4.5 J • 4.5 J/1 s = • 4.5 W

  11. A student lifts three 3 N books 0.5 m in 3 seconds. How much power did the student use? Compare this to the 4.5 W from the previous problem, which took 1 second. • (3 x 3 N) x 0.5 m = • 4.5 J • 4.5 J/3 s = • 1.5 W

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