Work, Energy and Power Flashcards
What is work done
The energy transfer required to provide motion to an object. Force * Distance moved in direction of force.
What is energy
The capacity to do work. Energy can be changed between forms
What is Kinetic Energy
Energy due to motion of an object with mass
What is gravitational potential energy
Energy of an object due ot its position in a gravitational field
What is chemical energy
Energy contained within the chemical bonds between atoms - released when the atoms are rearranged
What is elastic potential energy
Energy stored in an object as a result of reversible
change in its shape
What is meant by potential in physics
Stored energy
What is the principle of conservation of energy
The total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another.
How do you derive the formula for kinetic energy
𝑣2 = 𝑢2 + 2𝑎s. Taking initial velocity as 0, we get 𝑣2 = 2as. Rearranging to make s the subject gives s = 𝑣2/2a. Work done = Force * distance. Force is equal to mass * acceleration. Subbing this into formula for displacement we get ma𝑣2/2a. Acceleration cancels and left with 1/2m𝑣2.
How to calculate the change in GPE in a uniform gravitational field
E = mass * gravity * height. Lifting an object in a gravitational field requires a force equal to its weight - mg, and it travels a distance by being lifted - height. Work done = Force * Distance, therfore E = mg (force) * h( distance).
What happens between Ke and Gpe of an object moving up and down in a gravitational field with no resistive forces
In a closed system with no external energy transfer, as the object falls down, GPE is converted to KE. As the object rises up, KE is converted to GPE. Since KEmax = GPEmax, mgh = 1/2m𝑣2. 2gh = 𝑣2. V = Sqrt(2gh). The mass of the object does not affect its final speed.
What is Power
Rate of work done. Work Done / Time. Also given by Force * Velocity
Define efficiency
Useful output / Total output * 100
Define the watt
1 joule of work done per second
