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Chapter 7 Work and Energy

Chapter 7 Work and Energy. Study guide is posted online under homework. Problem 29.

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Chapter 7 Work and Energy

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  1. Chapter 7 Work and Energy Study guide is posted online under homework

  2. Problem 29 29.(II) What will a spring scale read for the weight of a 53-kg woman in an elevator that moves (a) upward with constant speed 5.0 m/s, (b) downward with constant speed 5.0 m/s, (c) upward with acceleration 0.33 g, (d) downward with acceleration 0.33 g, and (e) in free fall?

  3. 6-4 Satellites and “Weightlessness” More properly, this effect is called apparent weightlessness, because the gravitational force still exists. It can be experienced on Earth as well, but only briefly:

  4. HW4- Problem 32 32.(II) A window washer pulls herself upward using the bucket–pulley apparatus shown in Fig. 4–36. (a) How hard must she pull downward to raise herself slowly at constant speed? (b) If she increases this force by 15%, what will her acceleration be? The mass of the person plus the bucket is 72 kg.

  5. HW4 problem 54 54. (III) Suppose the pulley in Fig. 4–46 is suspended by a cord C. Determine the tension in this cord after the masses are released and before one hits the ground. Ignore the mass of the pulley and cords.

  6. 7-1 Work Done by a Constant Force The work done by a constant force is defined as the distance moved multiplied by the component of the force in the direction of displacement: W= Fd cos θ If the force and the displacement are in the same direction θ =0 and W=Fd

  7. 7-1 Work Done by a Constant Force In the SI system, the units of work are joules: Work is a scalar As long as this person does not lift or lower the bag of groceries, he is doing no work on it. The force he exerts has no component in the direction of motion.

  8. FN Fdrag mg Total Work or Net Work • When more than one force acts on an object, the total work is the sum of the work done by each force. Airplane Example Another way to look at it is…. Airplane Example

  9. Question A boy pulls a sled across the snow 10 m. The work done on the sled by the normal force is • Positive • Negative • Zero Normal

  10. Question A boy pulls a sled across a level field of snow. The work done on the sled by gravity is Positive Negative Zero Gravity

  11. Question A boy pulls a sled across the snow 10 m. The work done on the sled by the Boy is • Positive • Negative • Zero Force Boy

  12. Question • A pendulum bob is swinging back and forth in an arc in the plane of the page as seen below. The Tension force is 20 N, and the arc length is 5 m. • The Work done by the Tension force in one quarter swing (up or down) is • A) Positive • B) Negative • C) Zero • D) Depends on the direction of the swing FT

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