Chapter 10 - Work, energy, and power Flashcards
When a force acts on an object and makes it move we say that…
…work is done.
What are the equations for Work Done?
W = Fs
when the force is acting along the direction of motion.
W = Fscosθ
What is represented by the area under the line of a force-distance graph?
Work Done
What is the equation for Kinetic energy?
Ek = 1/2 x mv^2
What is the equation for change of gravitational potential energy?
ΔEp = mgΔh
What is the principle of conservation of energy?
Energy cannot be created or destroyed.
For an object descending through a vertical distance Δh, if the resistive forces on it are negligible, its gain of kinetic energy is…
…equal to its loss of potential energy.
1/2 x mv^2= mgΔh
For an object descending through a vertical distance Δh, if the resistive forces on it are not negligible, its final kinetic energy is…
…less than its initial potential energy because work is done by the resisitive forces.
1
— mv^2 = mgΔh - W
2
Therefore,
1
W = mgΔh - — x mv^2
2
What is power?
The rate of work done or the rate of energy transfer.
What are the equations for efficiency?
Efficiency = useful energy/power output divided by total energy/power input
The output power of a engine =
The output power of a engine = Energy per second wasted due to resistive forces + Gain of kinetic energy per second
What is energy?
The capacity to do work.
What is gravitational potential energy?
The energy due to the position of an object in another object’s gravitational field.
As two masses attract, work must be done to pull them apart and so the objects gain GPE.
