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Announcements

Announcements. *3 rd Exam on Thursday, November 3 rd * Homework for tomorrow… (Ch. 9, Prob 38, 49, & 59) 9.28: a) 314 J b) -155 J c) 0J d) 159 J Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm

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Announcements

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  1. Announcements • *3rd Exam on Thursday, November 3rd * • Homework for tomorrow… (Ch. 9, Prob 38, 49, & 59) 9.28: a) 314 J b) -155 J c) 0J d) 159 J • Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm • Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm

  2. Chapter 9 Kinetic Energy & Work (Power)

  3. Review… • The scalar product • Work done by a constant force (in more than 1D) • Work done by a variable force (in more than 1D)

  4. Problem 9.47a A 1.5 kg block is initially at rest on a horizontal frictionless surface when a horizontal force in the positive direction of an x axis is applied to the block. The force is given by F(x) = (2.5 N - x2 N/m2 )î, where x is in meters and the initial position of the block is x = 0.0 m What is the kinetic energy of the block as it passes through x = 2.0 m?

  5. Section 9.10: Power • Average Power is work done in a time t • Instantaneous Power is the instantaneous rate of doing work • What are the units of Power?

  6. Power continued… • For a particle moving along a straight line, Instantaneous Power can also be written as.. • Power is the rate at which the applied force does work.

  7. Human Energy Consumption

  8. Quiz Question 1 An escalator is used to move 20 people (~60 kg each) per minute from the 1st floor of a department store to the 2nd floor, h = 5m above. The power required is approximately? • 100 W • 200 W • 1000 W • 2000 W • 60,000 W h 30

  9. Quiz Question 2 What is the power output of a 70 kg sprinter who accelerates from rest to 10 m/s in 3.0 s? • 120 W • 230 W • 1200 W • 2100 W • 10,500 W

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