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Work

Work. Work : using a force for a distance W = F x d The work done by forces on an object = changes in energy for that object. Work and Energy are measured in Joules 1 Joule=1 Newton • meter. 42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?

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Work

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  1. Work • Work: using a force for a distance • W = F x d • The work done by forces on an object = changes in energy for that object. • Work and Energy are measured in Joules • 1 Joule=1 Newton • meter

  2. 42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N? F 300 J G 750 J H 1,000 J J 15,000 J Use the formula Work = Force x distance Force of 20 N x 15 meters = 300 Joules Answer:

  3. 6 Types of simple machines • Some Simple Machines: • Inclined planes • Screws • Pulleys • Wheel and axle • Levers • Wedge

  4. Why use a machine? • In an ideal (perfect) machine the work put into the machine (Win) = the work put out by that machine (Wout)

  5. Machines make work easier • The ideal mechanical advantage of a machine (IMA) of a machine is the number of times the output force is larger than the input force IMA=Fout/Fin • A machine can only make this happen by moving the input force through a farther distance than the output force • Fin • din=Fout • dout

  6. 48 The diagram shows an electric motor lifting a 6 N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat? F 9 J G 12 J H 18 J J 21 J

  7. Work Input = 30J done by the motor Work Output = Resistance Force x Resistance Distance Workout = 18J = 6N x 3m The difference is lost as heat due to friction, which is 30J – 18J = 12J Answer G

  8. Real Machines use Energy • No real machine is 100 % efficient. i.e. none put out more work than is put in • Efficiency of a machine is work output/work input X 100 % • Eff = WoutX 100% Win

  9. Machines use power • Power: the rate at which energy is used (work is done) • P=Work/time • Power is measured in H.P. or watts • 1 watt = 1 Joule 1 sec

  10. 45 If a force of 100 newtons was exerted on an object and no work was done, the object must have — A accelerated rapidly B remained motionless C decreased its velocity D gained momentum Work = Force x Distance Work = 0 Force = 100 N so 0 J = 100 N x d distance must be 0 It did not move!

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