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Power

Power. “Quiz” Tomorrow. 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. 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. You lift two 4 N books 2 m/s. How much power did you use? (4N + 4N) x 2m =

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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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