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CH 5 Lecture

CH 5 Lecture. FORCE. DISTANCE. WORK =. The two requirements: 1. 2. Something must move. Force must be in same direction as movement. Joules. The unit to measure work is ___________. Example: How much work is done if the guy pushes with 40 N to

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CH 5 Lecture

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  1. CH 5 Lecture

  2. FORCE DISTANCE WORK = The two requirements: 1. 2. Something must move Force must be in same direction as movement Joules The unit to measure work is ___________ Example: How much work is done if the guy pushes with 40 N to move the 20 N box 4 m?

  3. FORCE DISTANCE WORK = The two requirements: 1. 2. Something must move Force must be in same direction as movement Joules The unit to measure work is ___________ Example: How much work is done if the guy pushes with 40 N to move the 20 N box 4 m?

  4. work time POWER = Watts The unit to measure power is _________________ Example: What is the power needed to raise a 30 N object 3 m in 4 sec?

  5. ________________ - Energy of motion KINETIC ENERGY KE = ½ mv2 Kinetic energy (Joules) Mass (kilograms) Velocity (m/s)

  6. ________________ - Stored energy POTENTIAL ENERGY GRAVITATIONAL CHEMICAL ELASTIC PEgrav = mgh PEspring = ½ kx2 spring constant elongation mass 9.8 height

  7. KINETIC ENERGY POTENTIAL ENERGY WORK HEAT SOUND ALL ENERGY CAN BE ACCOUNTED FOR TOTAL ENERGY IS CONSERVED Changes from one form to another……….. All measured in JOULES What are the FUNDAMENTAL UNITS that make up a JOULE?

  8. v? A NO FRICTION Energy is conserved ………… EA = EB 3 m PEgrav = KE B mgh = ½ mv2 (9.8)(3) = ½ v2 v = 7.67 m/s

  9. A v? NO FRICTION Energy is conserved ………… B 3 m EA = EB 1.4 m PEgrav = KE + PEgrav mghA = ½ mv2 + mghB (9.8)(3) = ½ v2 + (9.8)(1.4) v = 5.61 m/s

  10. NO FRICTION B A ????? 3 m Ball CAN’T roll higher than 3 m ….…unless you add more energy

  11. What happened to the ENERGY?!? Jumping Spring Thing NO E Do Work PEelastic KE KE + PE PEgrav KE + PE NO E

  12. Picture Problems Energy is the SAME at all positions unless……. - Energy is ADDED - Energy is DISSIPATED Something does work ON it turns into sound or heat lost to work against friction. Not really LOST

  13. 8 m/s ? m/s 2m  = .200 EA - Efriction = EB Picture Problems ½ mv2 - Ffd = ½ mv2 ½ m(8)2 - (.200)(9.8m)(2) = ½ mv2 A B v = 7.49 m/s

  14. ? Picture Problems 3 kg EA = EB Compressed 8cm k = 480 N/m PEgrav PEspring = ½ k x2 = mgh ½ 480 (.08)2 = (3)(9.8)h

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