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Energy, Work and Power

Energy, Work and Power. A teacher applies a force to a wall and becomes exhausted. Did they do work?. Yes No. A book falls off a table and free falls to the ground. Was work done?. Yes No.

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Energy, Work and Power

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  1. Energy, Work and Power

  2. A teacher applies a force to a wall and becomes exhausted. Did they do work? • Yes • No

  3. A book falls off a table and free falls to the ground. Was work done? • Yes • No

  4. A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. Did they do work? • Yes • No

  5. A rocket accelerates through space. Did it do work? • Yes • No

  6. When a book falls to the ground, • Work is done on the system (book) • Work is done by the system (on the environment) • No work is done.

  7. Work-Energy Theorem (cont.) energy Environment System work Work done by system (-W) = decreases energy Work done on the system (+W) = increases energy

  8. Work done on system environment distance F system system W is + (increase energy)

  9. Work done by system system environment distance F system W is - (decrease energy)

  10. When pushing a lawn mower, how much of the force is inthe direction of the motion? • All of the force • Only the y component of the force • Only the x component of the force

  11. Calculate the work for each diagram 735J 500J 433J

  12. If an object gains 25 Joules of energy, how much work was done on the object? • No work • 12.5 Joules • 25 Joules • 50 Joules • Not enough information is given to determine the work done

  13. If Johnny lifts a 0.61 kg crate 2.0 meters in 4.0 s, how much power has he generated? • 0 Watts • 0.31 Watts • 2.0 Watts • 3.0Watts • 4.0 Watts • 12Watts • 48 Watts

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