Mechanics: Work, Energy and Power Flashcards
Principle of conservation of energy?
Energy cannot be created or destroyed.
Energy is measured in J. What is 1J?
1J = the energy needed to raise 1N weight through a vertical height of 1m.
What is work done?
W = F x d
Work done = force x distance moved in the direction of the force.
What is kinetic energy?
The energy of an object due to its motion.
Ek = 0.5 x m x v^2
What is potential energy?
The energy of an object due to its position.
Pendulum bob’s loss in Ep from its maximum height, h0?
Ep = 0.5 mv^2 = mg (h0 - h)
Work done to overcome friction?
W = mgh - 0.5mv^2
Energy can be transferred from one object to another by means of ? (3)
1) Work done, by a force due to one object making the other object move.
2) Heat transfer, from a hot object to a cold object. Can be due to conduction, convection or radiation.
3) Also, electricity, sound waves, and em radiation transfer energy.
What is power?
The rate of transfer of energy.
What is motive power?
The output power of an engine.
When a powered object moves at a constant velocity and height, resistive forced = - motive force. What does this say about work done by engine?
Work done by engine is transferred into internal energy of the surroundings by the resistive forces.
For a powered vehicle driven by a constant force, F moving at speed, v ..
W/s = F x d/s
Output power of engine, P = Fv
The motive power in terms of wasted energy and kinetic energy is?
Motive power = energy per second wasted due to the resistive force + the gain of Ek per second.
What is useful energy?
Energy transferred for a purpose.
What is the efficiency equation?
= useful energy transferred / energy supplied
= work done by the machine/energy supplied to the machine
