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Questions to consider

Questions to consider. What do we mean by “work” in science? What is the relationship between work and energy? What happens to work done against friction?. Outcomes:. You must be able to explain what is meant by “work done”.

meaghan-hamilton
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Questions to consider

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  1. Questions to consider • What do we mean by “work” in science? • What is the relationship between work and energy? • What happens to work done against friction?

  2. Outcomes: • You must be able to explain what is meant by “work done”. • You should be able to calculate work done when a force moves an object through a distance. • You could be able to rearrange the equation to solve more complicated problems.

  3. work done = energy transferred work done = force x distance moved w f d The basics • Previously... • If we apply a force to an object we can calculate the work done using the following equation...

  4. work done = force x distance Calculating work done question 1 A cyclist peddles a bicycle with a force of 1,000N moving it 250m. How much work has been done by the cyclist? = 1,000 x 250 = 250,000J = 250kJ

  5. work done force distance = Calculating work done question 2 A car engine moves a car with a force of 10kN and does 500kJ of work. How far has the car travelled? work done = force x distance = 500,000 / 10,000 = 50m

  6. work done = force x distance moved work done = weight x height increase = mass x gravity x height Furthermore... • We can use this equation to calculate gravitational potential energy.

  7. From the textbook • Read page 210-211 in full. Make sure you understand each point. Be sure to read the final section “Friction at work”. • Calculate the work done in the scene below.

  8. Work, force, distance calculations

  9. Outcomes: • You must be able to explain what is meant by “work done”. • You should be able to calculate work done when a force moves an object through a distance. • You could be able to rearrange the equation to solve more complicated problems.

  10. Last time... • You learnt that work done was equal to the amount of energy transferred. • work done = force x distance moved • You also used an equation to calculate the gravitational potential energy. • If the mass of the diver is 80 kg and the diving board is 30 meters high, what is the divers potential energy?

  11. Outcomes: • You must be able to state the kinetic energy equation. • You should be able to explain what is meant by conservation of energy and give examples. • You could be able to use the kinetic energy equation to solve a variety of problems.

  12. Feeling energetic? Who has the most kinetic energy: The girl or the cat?

  13. What is kinetic energy? The word ‘kinetic’ comes from the Greek word ‘kinesis’, meaning motion. Kinetic energyis the energy an object has because it is moving. All moving things have kinetic energy, but the amount of energy they have is not just dependent on how fast they are moving. What other factors affect the kinetic energy of a moving object?

  14. KE = ½ x mass x velocity2 = ½mv2 How is kinetic energy calculated? The kinetic energy (KE) of an object can be calculated using this equation: • Mass is measured in kilograms (kg). • Velocity is measured in metres per second (m/s). • KE is measured in joules (j).

  15. Calculating kinetic energy question A car with a mass of 1,500kg travels at a velocity of 20m/s. What is the kinetic energy of the car? kinetic energy = ½ xmass x velocity2 = ½ x 1,500 x 202 = 300,000J = 300kJ

  16. KE = ½mv2 Ö 2KE m 2KE v2 v = m = Rearranging the KE equation Sometimes it is necessary to rearrange the kinetic energy equation in order to calculate the mass or the velocity of a moving object. What are the rearranged versions of this equation for calculating mass and velocity?

  17. Ö 2KE mass velocity = Ö 2 x 2,250,000 20,000 = Calculating velocity question A lorry has a mass of 20,000kg. If its kinetic energy is 2.25mJ, at what velocity is it travelling? KE = ½ xmass x velocity2 = 15m/s

  18. Energy transfer of falling objects What happens to the KE and GPE of a rollercoaster?

  19. GPE lost = KE gained The relationship between GPE and KE The law of conservation of energy means that as an object falls, the GPE it loses must turn into a different form. This is only true if air resistance and friction are ignored. In reality, GPE would also be transferred into heat and sound energy so the KE of rollercoaster would be less than the GPE lost.

  20. Outcomes: • You must be able to state the kinetic energy equation. • You should be able to explain what is meant by conservation of energy and give examples. • You could be able to use the kinetic energy equation to solve a variety of problems.

  21. Extension question • Calculate the potential energy, kinetic energy, mechanical energy, velocity, and height of the skater at the various locations.

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