Edexcel A Level Physics:复习笔记2.20 The Principle of Conservation of Energy

• The principle of conservation of energy is a law of Physics which always applies to a closed system

• To apply conservation of energy, heat losses are usually ignored during the calculation stage
• In reality there are always some energy losses from the system
  • These should be mentioned when comparing calculated, ideal values to real-life situations

• Conservation of energy is often applied in questions about exchanges between kinetic energy and gravitational energy
• Common examples include:
  • A swinging pendulum
  • Objects in free fall
  • Sports such as skiing or skydiving where gravity is causing motion and few drag forces apply

• The gravitational potential energy stored initially is transferred to kinetic energy, or vice versa
• This allows either;
  • Final velocity to be found from the distance the object moved, or
  • Height of a drop from the final velocity

Step 1: Write down the known quantities

• • Vertical height, h = 750 sin 25°
  • Ek = 0.85 Ep

   

Step 2: Equate the equations for Ek and Egrav

Ek = 0.85 Egrav

½ mv2 = 0.85 × mgh

Step 3: Rearrange for final speed, v

Step 4: Calculate the final speed, v