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Physics Chp 5

Physics Chp 5. Work is done when a force acts to displace an object. Units are Nm which is also J W = Fd but the force and displacement have to be parallel to eachother . W = Fdcos θ the angle used is between F and d.

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Physics Chp 5

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  1. Physics Chp 5

  2. Work is done when a force acts to displace an object. Units are Nm which is also J • W = Fd but the force and displacement have to be parallel to eachother. • W = Fdcosθ the angle used is between F and d

  3. How much work does it take by your arm to lift a 0.5 kg book 1 m up off of the table? • How much does your arm do walking 5 m to the door?

  4. W = Fd • W = (0.5kg)(9.8m/s2)(1m) • W = 4.9 Nm • W = 0 the arm doesn’t do any force in the direction of the door.

  5. If you pull a 15 kg child on a sled using a force of 25 N at 30o above the horizontal, how much work do you do in the first 5 m? • W = Fdcosθ • W = (25N)(5m)cos(30o) =

  6. Kinetic Energy • KE= 1/2mv2 • Potential Energy • PEg= mgh • PEel= 1/2kx2 k is called the spring constant

  7. Mechanical Energy • ME = KE + PE • Conservation of Mechanical Energy • MEf = MEi

  8. If friction is present then Mechanical Energy is not conserved.

  9. If a 0.5 kg ball drops from a 30 m high building, how fast does it hit the ground? • PE = mgh KE = ½ mv2 • ME = PE + KE and MEo = MEf • PEo = KEf • (0.5kg)(9.8m/s2)(30m) = ½ (0.5kg)(v2) • v= 24 m/s

  10. Work – Kinetic Energy Theorem • Wnet = ∆KE Wnet = Fnet d • Power P= W/t Nm/s or J/s or W for watts • or P = Fv

  11. Ex. How much work could a 100 W light bulb do in 1 minute if it was all useable? • P = W/t 100 W = W / 60s W = 6000 Nm

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