1 / 7

Mechanical Energy

Mechanical Energy. Net Work. The work-energy principle is D K = W net . The work can be divided into parts due to conservative and non-conservative forces. Kinetic energy D K = W con + W non. d. F f. F g. Kinetic and Potential Energy.

wade-greene
Download Presentation

Mechanical 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. Mechanical Energy

  2. Net Work • The work-energy principle is DK = Wnet. • The work can be divided into parts due to conservative and non-conservative forces. • Kinetic energy DK = Wcon + Wnon d Ff Fg

  3. Kinetic and Potential Energy • Potential energy is the negative of the work done by conservative forces. • Potential energy DU = -Wcon • The kinetic energy is related to the potential energy. • Kinetic energy DK = -DU+ Wnon • The energy of velocity and position make up the mechanical energy. • Mechanical energy Emech = K + U

  4. Conservation of Energy • Certain problems assume only conservative forces. • No friction, no air resistance • The change in energy, DE = DK + DU = 0 • If the change is zero then the total is constant. • Total energy, E = K + U = constant • Energy is not created or destroyed – it is conserved.

  5. The spring force is conservative. U = ½ kx2 The total energy is E = ½ mv2 + ½ kx2 A 35 metric ton box car moving at 7.5 m/s is brought to a stop by a bumper. The bumper has a spring constant of 2.8 MN/m. Initially, there is no bumper E = ½ mv2 = 980 kJ Afterward, there is no speed E = ½ kx2 = 980 kJ x = 0.84 m Springs and Conservation v x

  6. A 30 kg child pushes down 15 cm on a trampoline and is launched 1.2 m in the air. What is the spring constant? Initially the energy is in the trampoline. U = ½ ky2 Then the child has all kinetic energy, which becomes gravitational energy. U = mgh The energy is conserved. ½ ky2 = mgh k = 3.1 x 104 N/m Energy Conversion

  7. Solving Problems • There are some general techniques to solve energy conservation problems. • Make sure there are only conservative forces and kinetic energy in the problem • Identify all the potential and kinetic energy at the beginning • Identify all the potential and kinetic energy at the end • Set the initial and final energy equal to one another next

More Related