Work and Energy - Mission WE8 Detailed Help

The path of a pendulum bob moving to and fro is shown in the diagram below. Frictional forces can be assumed to be negligible. Perform an energy analysis and fill in all the blanks.


An energy analysis begins by first identifying which types of forces are doing net work upon the object. In the case of the pendulum, frictional forces (friction and air resistance) are said to be negligible. The tension force acts perpendicular to the pendulum's motion and does not do work upon the pendulum. So gravity - a conservative force - is the only force doing work upon the pendulum.

Since the only work being done on the pendulum is being done by a conservative force, the total mechanical energy will be conserved. See Know the Law section. The amount of total energy - KE plus PE - at the beginning of the motion will be the same amount at every location along the path of the pendulum. Using these principles, all blanks can be determined.

Energy Conservation:
If the only forces doing net work upon an object are conservative forces (such as gravity and spring forces), then the mechanical energy of the object will be conserved. The energy may change from one form to another - potential to kinetic or vice versa; but the total amount of the two forms together will be unchanging.