Physics Chapter 6 Concepts
Some of the following situations are consistent with the principle of conservation of mechanical energy, and some are not. Which ones are consistent with the principle?
An object moves uphill with a decreasing speed.An object moves downhill with an increasing speed.
Kinetic Energy
Energy associated with motion
The Principle of Conservation of Energy
Energy can neither be created not destroyed, but can only be converted from one form to another.
Engine A has a greater power rating than engine B. Which one of the following statements correctly describes the abilities of these engines to do work?
Engine A and B can do the same amount of work, but A can do it more quickly.
A rocket is at rest on the launch pad. When the rocket is launched, its kinetic energy increases. Is the following statement true or false? "The amount by which the kinetic energy increases is equal to the work done by the force generated by the rocket's engine."
False
Conservative Energy Forces
Gravitational Force Elastic Spring Force Electric Force
A rope is tied to a tree limb and used by a swimmer to swing into the water below. The person starts from rest with the rope held in the horizontal position, swings downward, and then lets go of the rope. Three forces act on him: his weight, the tension in the rope, and the force due to air resistance. His initial height h0 and final height hf are known. Considering the nature of these forces, conservative versus non-conservative, can we use the principle of conservation of mechanical energy to find his speed vf at the point where he lets go of the rope?
If Wnc= 0 (work due to nonconservative forces) conservation of energy Tension and air resistance --- non conservative T is always r to the circular path So no work done by T. Work done by air resistance is nonzero. So ideally no.
A satellite is moving about the earth in a circular orbit and an elliptical orbit. For these two orbits, determine whether the kinetic energy of the satellite changes during the motion
In circular motion, F/ S always no work done. KE changes in the elliptical orbit, but not in the circular orbit.
Work
Joule (J)
Force
Newton (N)
Nonconservative Forces
Static and kinetic frictional forces Air resistance Tension Normal Force Propulsion force of a rocket
Work-Energy Theorem
The relationship that relates work to the change in kinetic energy
Principle of Conservation of Mechanical Energy
The total mechanical energy (E = KE + PE) of an object remains constant as the object moves, provided that the network done by external nononservative forces is zero.
A suitcase is hanging straight down from your hand as you ride an escalator. Your hand exerts a force on the suitcase and this force does work.Which one of the following statements is correct?
The work is positive when you ride up the escalator and negative when you ride down the escalator.
Conservative Force
Version 1 A force is conservative when the work it does on a moving object is independent of the path between the object's initial and final positions. Version 2 A force is conservative when it does no work on an object moving around a closed path, starting and finishing at the same point.
Power
Watt (W)
Average Power
rate at which work is done, and it is obtained by dividing the work by the time required to perform the work
Gravitational Potential Energy
the energy that an object of mass m has by virtue of its position relative to the surface of the earth. That position is measured by the height h of the object relative to an arbitrary zero level
