P 12 - Energy Flashcards
What is the relation between energy transferred to an object and the work done by the force?
Energy transferred = work done
Equation for work done
W = force applied(N) x distance moved along the line of action of a force.(m)
W = f x s
What happens when an object moves upwards?
The GPE store increases. This increase is equal to the work done by he force acing on it.
What happens when an object moves downwards?
It’s energy in the GPE store decreases. This decrease is equal to the work done by the gravitational force acting on it.
The work done when an object moves up or down depends on:
- How far its moved in height ( change in height )
- Its weight.
What is power?
The amount of energy transferred each second.
To work out power:
P = Energy transferred to appliance / time taken for transfer. P = E/t
What is wasted energy?
Energy given to the surroundings, that doesn’t give the purpose of the contraption.
To work out efficiency of a device
Efficiency =
Useful energy transferred by device / total energy supplied to device.
Efficiency = output / input X 100 to get %
To work out kinetic energy
Kinetic energy = 1/2 X mass X speed^2
Ek = 1/2 m v^2
To work out elastic potential energy
EPE = 1/2 x spring constant (N/m) x extension^2 (m)
Ee = 1/2 x k x e^2
To work out change in GPE =
Change in GPE =
mass (kg) x gravitational field strength (N/kg) x change in height (m)
M x g x change in height
To work out spring constant
EPE / 1/2 x extension^2
K =
Ee
1/2 x e^2
To work out extension
Square root of:
Ee
1/2 x k
Equation linking energy transferred to specific heat capacity
Heat energy transferred =
Mass X specific heat capacity X temp change
