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ENERGY

ENERGY. ENERGY A BODY HAS BECAUSE OF ITS POSITION OR CONDITION. P.E.= E p = mgh. G .P.E. = weight x height. mv 2. KE. 2. KINETIC ENERGY ( E k ) = ½ mv 2. =. POTENTIAL ENERGY. ENERGY A BODY HAS BECAUSE OF ITS POSITION OR CONDITION. P.E.= E p = mgh. G .P.E. = weight x height.

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ENERGY

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  1. ENERGY

  2. ENERGY A BODY HAS BECAUSE OF ITS POSITION OR CONDITION P.E.= Ep = mgh G.P.E. = weight x height

  3. mv2 KE 2 KINETIC ENERGY (Ek) = ½ mv2 =

  4. POTENTIAL ENERGY

  5. ENERGY A BODY HAS BECAUSE OF ITS POSITION OR CONDITION P.E.= Ep = mgh G.P.E. = weight x height

  6. EXAMPLE What is the p.e. of a book of mass 1200 g, resting on a shelf 2 m above the ground? p.e. = mgh p.e. = 1.2kg x 10m/s/s x 2m p.e. = 12.0 N x 2 m p.e. = 24 N-meter or Joules

  7. SAMPLE PROBLEM: A hiker weighing 680 N climbs 40 m up a hill. Calculate the gravitational potential energy gained at the top of the climb. Ep= mgh

  8. P.E.=Ep= mgh Ep = 680 N x 40m = 27,200 N-m or 27.2 KJ

  9. 1. Calculate the p.e. of a 40 kg iron bar raised 1 m. (g = 10m/s/s) 2. Calculate the p.e. of a 65 kg boulder resting at 22 m above the road. 3. A 200 g jar falls from a height 1.5 m onto the floor. Calculate the p.e. of the jar before the fall.

  10. ANSWERS 1. Calculate the p.e. of a 40 kg iron bar raised 1 m. 400 N-m or 400J 2. Calculate the p.e. of a 65 kg boulder resting at 22 m above the road. 14,300 N-m or 14.3 KJ 3. A 200 g jar falls from a height 1.5 m onto the floor. Calculate the p.e. of the jar before the fall. 3 J

  11. POTENTIAL ENERGY Ep or p.e. is the potential energy an object has because of its height. “The higher an object is lifted, the greater its p.e.” “The greater the mass of an object the greater its p.e.” the gain in p.e. = work doneEp = W

  12. gain in p.e. = work done Ep = W Remember: W = F x d where the lifting force is m x g (F= ma) (m = mass, g = acceleration due to gravity)

  13. Putting these formulae together: Gain in Potential energy= work done lifting Ep = W = lifting force x distance lifted (height)Ep = F x d (h) = weight force x distance lifted Ep = Fg x d (h) (g = 10N/kg) = mass of object x g x distance liftedEp = mgh

  14. mv2 KE 2 KINETIC ENERGY (Ek) = ½ mv2 =

  15. KINETIC ENERGY • Kinetic energy Ek or k.e. is the • energy that an object has because it • is moving • The unit of measure for k.e. is joule • The greater the speed the greater the • k.e. of the object • The greater the mass of a moving • object, the greater the k.e. of the • object

  16. What is the Ek of an arrow weighing 25 gm traveling at 25m/s?

  17. What is the Ek of an arrow weighing 25 gm traveling at 25m/s? Answer: k.e. = ½ mv2 = ½ x .025kg x 25m/s2 = ½ x 0.025kg x 625m/s = (0.5) 15.625 = 7.8125 Nm but 1 Nm = 1J = 7.8125 J

  18. Potential Energy = Weight x Height (P.E. = w x h) or Ep= mgh Kinetic Energy = ½ Mass x Velocity2 (K.E.= 1/2mv2) weight = mg Units: Energy = joules (J) Weight = newtons (N) Mass = kilograms (kg) Velocity = m/s Height = meters (m) Gravity constant = 9.8m/sec/sec Work = joules 1km = 1000m 1kg= 1000g 1hr= 3,600sec

  19. Energy cannot be created nor destroyed. Energy is converted from one form to another.

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