PHY101_Chap5Fall09

PHY101_Chap5Fall09 - Chapter 5 ENERGY 5.1 Work Work = F x...

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Chapter 5 ENERGY

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5.1 Work Work = F. Δ x
5.1 Work • The work, W , done by a constant force on an object is defined as the product of the component of the force along the direction of displacement and the magnitude of the displacement • This gives no information about – the time it took for the displacement to occur – the velocity or acceleration of the object • Work is a scalar quantity

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A worker pushes a sled with a force of 40 N over a level distance of 6.0 m. If a frictional force of 24 N acts on the wheelbarrow in a direction opposite to that of the worker, what net work is done on the wheelbarrow? 1. 240 J 2. 216 J 3. 144 J 4. 96 J Quiz Qn. 3
Work – F is the magnitude of the force Δ x is the magnitude of the object’s displacement θ is the angle between

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Work done example The total mass of fish and sled = 50 kg. F = 120 N and he pulls it for 5 m. How much work is done if θ = 0 How much work is done if θ = 30 o
When Work is Zero • Displacement is horizontal • Force is vertical • cos 90° = 0

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Work Can Be Positive or Negative • Work is positive when lifting the box • Work would be negative if lowering the box – The force would still be upward, but the displacement would be downward
Work – F is the magnitude of the force Δ x is the magnitude of the object’s displacement θ is the angle between

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5.2 Kinetic Energy • Energy associated with the motion of an object • Scalar quantity with the same units as work • Work is related to kinetic energy
5.2 The Work-Energy Theorem and Kinetic Energy • Energy: when work is done, energy changes • Many forms of energy: chemical energy, nuclear energy, electric/magnetic energy, mechanical energy … – Total energy is conserved • Energy can do things

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• An object’s kinetic energy can also be thought of as the amount of work the moving object could do in coming to rest – The moving hammer has kinetic energy and can do work on the nail
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PHY101_Chap5Fall09 - Chapter 5 ENERGY 5.1 Work Work = F x...

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