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=Chapter Eight- Energy  =

**Work is a produce of force and distance (W=Fd), measured in joules (J)**
Examples: Bobby pushes his grandma with 3 newtons of force. If he pushes her a distance of 4 meters from him, how much work is he exerting on grandma? (3 N)(4 M)=12 J

If grandma moves Bobby a distance of 3 meters and exerts 18 J of work, how much force is she exerting on Bobby? W/D=F (18 J)/(3 M)=6 N

Measured in watts (W), (J/s)
Examples: Willy exerts 100 J of work on his dog sled team. If it takes him 20 seconds to get to the finish line, how much power is he exerting? (P=W/t) (100 J)/(20 s)=5 W

Susan B. Anthony is traveling a distance of 52 meters on her horse and buggy (the horse exerting 7 N of force.) If she travels at this rate for 10 seconds, how much power is her horse exerting? W(Fd)/t=P (52 M)(7 N)/(10 s)=36.4 W

Energy-total amount of work done in an object, measured in joules
Two types of mechanical energy: kinetic and potential

It is a relative measurement, so you get to pick the height that will be your "zero level", just keep it the same throughout your calculations.
Examples: Roger throws Harold (Harry, if you please) in the air a distance of 8 meters. If Harold weighs 81 kg, what is his potential energy? PE=mgh (81 kg)(10 m/s)(8 m)=6,480 J

KE=1/2mv²
Examples: Lucy's mass is 8 kg. If she rolls down a hill with a velocity of 12 m/s, how much kinetic energy will she produce? KE=1/2mv² 1/2(8 kg)(12 m)² =576 J

Example: Willfred's kinetic energy is 370 J. If his mass is 87 kg, what is his velocty?

370=1/2(87)v²
v=2.94 m/s

Law of conservation of energy- states that energy cannot be created nor destroyed, only transfered from object to object or transformed to a different type of energy within the object.
The total amount NEVER changes In the absence of friction: PEi + KEi = PEf + KEf or mghi + 1/2mv²i = mghf + 1/2mv²f

Example: If you have a mass of 80 kg and run towards a wall at 15 m/s² and jump up one meter to kick it, how much energy must the wall get according to the conservation of energy?

(80 kg)(10m/s)(1 m) + 1/2(80kg)(15m/s²)=1400 J

Ideally, when no work is lost to friction:
Wout = Win or FoutDout = FinDin

Mechanical advantage is when the machine multiplies the force you put in to get the work it puts out.
MA=Fout/Fin

When there is no friction, the theoretical mechanical advantage is expressed as the ratio of the input and output distances
TMA= din/dout

The ratio of input and output work is better known as efficiency.
eff= Wout/Win or eff= MA/TMA