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?
1 2
Ek = — 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
— mv = mgΔh
2
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 2
— mv = mgΔh - W
2
Therefore,
1 2
W = mgΔh - — mv
2
What is power?
The rate of work done or the rate of energy transfer.
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 are the equations for efficiency
useful energy output
Efficiency = —————————————
total energy input
useful power output Efficiency = -------------------------------------
total power input
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.
What is kinetic energy?
The energy due to the movement of an object.
A vehicle moving at a constant velocity has motive force (driving force) =…
… motive force = resistive forces.
