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Mechanical Energy

Mechanical Energy. What is mechanical energy? the “something” that causes work to be done What kinds of mechanical energy are there? kinetic (associated with motion) potential (associated with elevation) Units - Joules. KE + PE = E. v=0. KE + PE = E.

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Mechanical Energy

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  1. Mechanical Energy • What is mechanical energy? • the “something” that causes work to be done • What kinds of mechanical energy are there? • kinetic (associated with motion) • potential (associated with elevation) Units - Joules

  2. KE + PE = E v=0

  3. KE + PE = E v=0 KE = 1/2 m v2 take m = 1.0 kg

  4. KE + PE = E v=0 0 KE = 1/2 m v2 take m = 1.0 kg

  5. KE + PE = E 5 m v=0 0 PE = m g h

  6. KE + PE = E 5 m v=0 0 50 50 Now, release the ball.

  7. KE + PE = E 5 m y v=0 0 50 50 ? ? ? y = 1m v0 = 0 m/s vf = ? ay = 10 m/s/s t = ? vf = 4.5 m/s

  8. KE + PE = E 5 m v=0 0 50 50 v=4.5 10 ? ? KE = 1/2 m v2 = 1/2 (1) (20) = 10 J

  9. KE + PE = E 5 m v=0 0 50 50 v=4.5 10 40 ? PE = m g h = (1) (10) (4) = 40 J

  10. KE + PE = E 5 m v=0 0 50 50 v=4.5 10 40 50

  11. KE + PE = E 5 m v=0 0 50 50 v=4.5 10 40 50 v=6.3

  12. KE + PE = E 5 m 20 30 50 v=0 0 50 50 v=4.5 10 40 50 v=6.3 Let’s Check

  13. KE + PE = E 5 m 20 30 50 v=0 0 50 50 v=4.5 10 40 50 v=6.3 KE = 1/2 m v2 = 1/2 (1) (6.3) 2 = 20 J

  14. KE + PE = E 5 m 20 30 50 v=0 0 50 50 v=4.5 10 40 50 v=6.3 Question: How fast will the ball be traveling when it is 1 m from the ground?

  15. KE + PE = E 5 m 20 30 50 50 40 10 v=0 0 50 50 v=4.5 10 40 50 v=6.3

  16. KE + PE = E 5 m 20 30 50 50 40 10 v=0 0 50 50 v=4.5 10 40 50 v=6.3 KE = 1/2 m v2

  17. KE + PE = E 5 m 20 30 50 50 40 10 v=0 0 50 50 v=4.5 10 40 50 v=6.3 40 = 1/2 (1) v2

  18. KE + PE = E 5 m 20 30 50 50 40 10 v=0 0 50 50 v=4.5 10 40 50 v=6.3 80 = v2

  19. KE + PE = E 5 m 20 30 50 50 40 10 v=0 0 50 50 v=4.5 10 40 50 v=6.3 v = 8.9 m/s

  20. A car (m=1000 kg) driving at 20 m/s goes over a ramp angled at 370 with height 5 m. How fast is the car traveling when it hits the ground 15 m below the end of the ramp? 5 m 15 m 370

  21. KE PE E KE PE E KE PE E A car (m=1000 kg) driving at 20 m/s goes over a ramp angled at 370 with height 5 m. How fast is the car traveling when it hits the ground 15 m below the end of the ramp? 5 m 15 m 370

  22. Problem • A 15 kg block on wheels is initially traveling 5 m/s. A force of 2 N pushes the block for 10 m. How much kinetic energy is there during this interval? 2 N 10 m

  23. KEf KEi Work Changes KE There is a change in kinetic energy which is what we call work. 1/2 m vf2 - 1/2 m v02 = F d The quantity F d is called the work!

  24. Problem • A 15 kg block on wheels is initially traveling 5 m/s. A force of 2 N pushes the block for 10 m. How much is the kinetic energy is there during this interval? Or how much work is done? Work = F Dx = (2 N) (10 m) = 20 Joules 2 N 10 m

  25. F KE x DKE is + F x KE DKE is - How does KE change?

  26. Work-out?

  27. How much work is done? T = 1000 N 37o

  28. How much work is done? T = 1000 N T = 1000 N 37o 37o Dx = 5m

  29. Power • Given: Aaron can do 5 billion joules of work! • Question: Is Aaron a powerful man?!? • Bigger question: Does it take Aaron a minute to do all this work, or the rest of his life? • Power is how much work Aaron can do in one second.

  30. joule watt = second Work Power = Dt DEnergy Power = Dt F Dx Dx Power = = F Dt Dt Power = F v

  31. 1000 joules kilowatt = second 1000 joules second kilowatt-hour ? hour = 3600 seconds kilowatt - hour = x 3600 sec = 3,600,000 joules

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