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The apple is …….

=. x. =. x. =. . :. Vel ocity. The apple is ……. =. . :. =. x. =. x. x. The apple is ……. P2.2.1 Forces and Energy - Objectives. Understand that if ‘work’ is done then a force is required. Energy is transferred when work is done (e.g. against frictional forces).

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The apple is …….

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  1. = x = x =  : Velocity The apple is …….

  2. =  : = x = x x The apple is …….

  3. P2.2.1 Forces and Energy - Objectives • Understand that if ‘work’ is done then a force is required. • Energy is transferred when work is done (e.g. against frictional forces). • How to calculate kinetic energy, power and potential energy.

  4. Work done • Work done, force and distance are related by the equation: W = F x d • W is the work done in joules, J • F is the force applied in newtons, N • d is the distance moved in the direction of the force in metres, m

  5. How much work is needed to push this plane 200m? 500N Force (to overcome friction) 200m in direction of force W = F x d = 500 x 200 = 100 000 Joules

  6. Q1. A car needs to be pushed 200m, the friction of the tyres on the road is 75N. What is the work done? Q2. 10000J of energy is used to move a ship 1m. What was the force of the water resistance?

  7. Power • Power is the work done or energy transferred in a given time. P = E / t P is the power in watts, W E is the energy transferred in joules, J t is the time taken in seconds, s

  8. What is the power of the plane engine if it transfers 5000J of energy in 5 seconds? P = E / t = 5000 / 5 = 1000 W

  9. Potential Energy • Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field. Ep= m x g x h • Ep is the change in gravitational potential energy in joules, J • m is the mass in kilograms, kg • g is the gravitational field strength in newtons per kilogram, N/kg • h is the change in height in metres, m

  10. How much potential energy does this plane have when it flies at 1000m altitude? Ep = m x g x h Ep = 1000 x 10 x 1000 Ep = 10 000 000 J 1000kg mass 1000m height g = 10 N/kg

  11. Kinetic Energy • The kinetic energy of an object depends on its mass and its speed. Ek= ½ m x v2 • Ek is the kinetic energy in joules, J • m is the mass in kilograms, kg • v is the speed in metres per second, m/s

  12. How much kinetic energy does this plane have when it flies at 50 m/s? 50m/s 1000kg mass Ek = ½m x v2 = ½ x 1000 x 502 =

  13. Momentum • Momentum is a property of moving objects: p = m x v • p is momentum in kilograms metres per second, kg m/s • m is the mass in kilograms, kg • v is the velocity in metres per second, m/s

  14. How much momentum does this plane have when it flies at 50 m/s? 50m/s 1000kg mass p = m x v p = 1000 x 50 p = 50 000 kg m/s

  15. Conservation of momentum The total momentum before an event is equal to the total momentum after the event.

  16. Conservation of momentum

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