1 / 8

Further Topics: Work & Energy

Further Topics: Work & Energy. Section 8.1. Reminders. Weekly Reflection #8 due on Tuesday evening. Online reading quiz due prior to the start of class on Thursday. LAB this week A7-CE : Conservation of Energy due in lab by Friday at 4 p.m.

ebony-haley
Télécharger la présentation

Further Topics: Work & Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Further Topics: Work & Energy Section 8.1

  2. Reminders • Weekly Reflection #8 due on Tuesday evening. • Online reading quiz due prior to the start of class on Thursday. • LAB this week A7-CE: Conservation of Energydue in lab by Friday at 4 p.m. • Quiz #4 on Thursday, October 23rd, addressing Chapter 8 (Work and Energy) and Chapter 9 (Gravitation).

  3. Work • Work is done only when energy is expended. • Physical work not same as physiological work. • Work is defined as force times distance, FΔd • Work causes a change in the energy of a body: • FΔd = ΔE (work-energy principle) • Impulse causes a change in momentum: • FΔt = mΔv (impulse-momentum principle)

  4. Mechanical Energy • Kinetic Energy = (½)mv2 • Gravitational potential energy = mgh • Elastic potential energy = (½)kx2 where k is the spring constant that has units of F/Δx • The unit of work or energy is the Nm or Joule, J • Like momentum, mechanical energy is always conserved. That is, Ei = Ef • It is “meaningfully” conserved only in “isolated” systems and in perfectly elastic collisions.

  5. Power • Power is the rate at which energy is produced or consumed. • P = energy transferred/unit time = E/t • The unit of power, Nm/s = J/s = Watt, W.

  6. An now some examples • Conservation of energy, Ei = Ef • A ball is tossed up into the air… • An amusement park cart collides with a spring… • A moving roller coaster reaches bottom… • Work FΔd= ΔE (work-energy principle) • A block slides under frictional force,f = μN= -μmg • Power = ΔE/t = W/t • How much power required to lift an elevator…

  7. Sample Problems #1 & #2 • A bullet is shot upward from with an initial speed of 55m/s. How high does it go? • #1: Use kinematics (equations of accelerated motion) to solve the problem. • #2: Use conservation of energy to solve the problem.

  8. Sample Problems #3 & #4 • A 0.005kg bullet moving horizontally with a speed of 330m/s hits a wooden block with a mass of 2.3kg that is suspended like a pendulum but with two V-strings. The bullet become imbedded in the wood. • #3: What is the speed of the block immediately after the bullet is embedded? • #4: How high do the block and bullet go?

More Related