Physics ENERGY

• Units of energy


  Not provided
• Principle of conservation of energy


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• Four different energy stores

  • Not provided
• Unwanted energy


  Not provided
• Unwanted energy is usually transferred to what energy store

  Not provided
• Energy store of a chocolate bar

  Not provided
• Energy store of a moving motorbike

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• Two energy stores of a moving aeroplane high in the sky

  • Not provided
• Energy store of a helicopter hovering (not moving)

  Not provided
• Energy store of a stretched elastic band

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• Energy store of petrol

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• Input and output energies for:

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• Roger Federer serves a tennis ball directly into the air. List all of the energy transfers that occur. Include the tennis ball returning to the ground, and then bouncing back up again.
• Andrew skis down a hill. Andrew starts from the top of the hill and his speed increases as he goes downhill. He controls his speed and direction by using his skis. He brings himself to a stop at the bottom of the hill. Describe the energy changes that happen between starting and stopping.
• A child drops a ball. The ball hits the ground and bounces. The graph shows the velocity-time graph for the ball from when the ball is dropped until when the ball reaches the top of its first bounce. Air resistance has been ignored. When the ball hits the ground, energy is transferred from the ball to the Earth. Explain how the data in the graph above shows this energy transfer.
• Power


  P = W/t
• Body armour is designed to resist penetration by projectiles
• The more kinetic energy that a projectile has, the greater its penetration
• British army issue body armour requires a minimum of 1,500 J of kinetic energy to penetrate it
• Your task is to find out which of a selection of different weapons would be a risk to penetrate the armour
• Gun type


  • M4A1 Carbine
  • Desert Eagle
  • Arctic Warfare
  • AK47
  • Beretta 92
  • FN P90
• Round type


  • 5.56×45mm NATO
  • .50 Action Express
  • 7.62×51mm NATO
  • 7.62×39mm
  • .40 S&W
  • FN 5.7x28mm
• Round mass (g)


  • 0.0041
  • 0.02
  • 0.0113
  • 0.008
  • 0.0107
  • 0.002
• Muzzle velocity (m/s)


  • 800
  • 430
  • 800
  • 641
  • 350
  • 716
• Kinetic energy (J)
• Objects with kinetic energy


  • Any moving object
• Kinetic energy equation


  KE = 1/2 mv^2
• Units


  KE: J, m: kg, v: m/s
• Gravitational field strength on Earth = 9.8 N/kg
• Calculating kinetic energy


  • Car: m = 1200 kg, v = 20 m/s, KE = 240,000 J

  1. Student: m = 55 kg, v = 0.6 m/s, KE = 9.9 J
  2. Runner: m = 62 kg, v = 0.8 m/s, KE = 19.84 J
  3. Tennis ball: m = 0.058 kg, v = 46 m/s, KE = 30.7 J
  4. Dog: m = 3.2 kg, v = 1.2 m/s, KE = 2.304 J
• Rearranging the kinetic energy equation to solve for mass
• Calculating mass


  • Automatic door: KE = 1.6 J, v = 0.2 m/s, m = 40 kg

  1. Wind turbine blade: KE = 104,040 J, v = 6 m/s, m = 2,867 kg
  2. Aeroplane: KE = 843,700 J, v = 75 m/s, m = 150 kg
  3. Canoe: KE = 5 J, v = 0.5 m/s, m = 20 kg
  4. Child on bike: KE = 1,224 J, v = 6 m/s, m = 34 kg
• Rearranging the kinetic energy equation to solve for velocity

  
• Calculating velocity


  • Bus: KE = 493,900 J, m = 5,040 kg, v = 10 m/s

  1. Lift: KE = 4,116 J, m = 4,200 kg, v = 0.5 m/s
  2. Bird: KE = 40.5 J, m = 0.25 kg, v = 18 m/s
  3. Wii remote: KE = 1.44 J, m = 4.5 kg, v = 0.4 m/s
  4. Hot air balloon: KE = 76,550 J, m = 1,890 kg, v = 2 m/s
• Bullet: m = 4.2 g, v = 1,700 mph, KE = 2,500 J
• Car: KE = 75,000 J, v = 10 m/s, m = 750 kg
• Bullet: m = 50 g, KE = 25,000 J, v = 1,000 m/s
• Truck: KE = 9,000,000 J, v = 40 m/s, m = 5,625 kg
• Man: Initial KE = 1,000 J, m = 100 kg, Final KE = 2,000 J, v = 1.4 m/s
• Eagle: KE = 2,800 J, v = 120 km/h, m = 2 kg