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 30 o above the horizontal, how much work do you do in the first 5 m? W = Fdcosθ W = (25N)(5m)cos(30 o ) =

6. Kinetic Energy KE= 1/2mv 2 Potential Energy PE g = mgh PE el = 1/2kx 2 k is called the spring constant

7. Mechanical Energy ME = KE + PE Conservation of Mechanical Energy ME f = ME i

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 mv 2 ME = PE + KE and ME o = ME f PE o = KE f (0.5kg)(9.8m/s 2 )(30m) = ½ (0.5kg)(v 2 ) v= 24 m/s

10. Work – Kinetic Energy Theorem W net = ∆KE W net = F net 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