Unit 3 - Lesson 13: Kinetic & Gravitational Potential Energy Flashcards
If an object gains gravitational potential energy (GPE) as its position increases with height, then the object falls/moves back down towards the ground, what will that GPE be transferred as & why? Can the energy be transferred back to GPE?
The GPE will be transferred as work (F x d) into making the object move i.e. transferring energy to its kinetic energy store. Equally, energy in the kinetic energy can be transferred back to GPE to increase the objects height.
The higher an object’s raised, the (more/less) potential it has.
The higher an object’s raised, the MORE potential it has.
When is energy transferred to an objects kinetic energy store and when is it transferred away from this store?
Energy is transferred to an objects kinetic energy store when it speeds up and away from this store when it slows down.
What does the conservation of energy tell us about the energy lost from the GPE?
Why might some energy be lost as thermal energy to the surroundings?
The conservation of energy tells us that the energy lost from the GPE store will equal the energy gained in the kinetic energy store. Basically, this means that no energy can be lost or used up, only moved from one store to another. It might not necessarily be a straight swap between GPE and kinetic. This would only apply in a vacuum. Some may be lost as thermal energy to surroundings due to air resistance.
What does the kinetic energy than an object has in its kinetic energy store depend on? There’s two things it depends on.
The objects MASS and its SPEED.
What is the equation to find ‘Energy in a kinetic energy store’?
Energy in kinetic energy store = 1/2 x mass x (speed)^2
KE = 1/2 x m x v^2
How can we rearrange this formula to find mass?
m = KE/(1/2 x v^2)
What method can we use to rearrange the formula: KE = 1/2 x m x v^2?
The triangle method.
KE is at the top of the triangle.
1/2 x m x v^2 are at the bottom of the triangle.
Remove the one you want to find from the triangle, then complete the equation.
What does the energy in a gravitational potential energy store depend on?
The mass of the object and its height.
What’s the gravitational field strength on Earth?
9.8 N/Kg
What is the formula to find ‘Energy in GPE store’?
Energy in GPE store = mass x gravitational field strength x height
GPE = m x g x h
Rearrange GPE = m x g x h to find m.
- GPE = m x g x h
- GPE/(gxh) = m x g x h/(g x h)
- GPE/(gxh) = m
- m = GPE / (g x h)
OR use the triangle method.
The top of the triangle is GPE.
The bottom of the triangle is m x g x h.
Remove the one you want to find.
Complete the equation.
What is GPE (gravitational potential energy) equal to?
GPE = KE (kinetic energy)
What is mgh (mass x gravitational field strength x height) equal to due to GPE = KE?
mgh = 1/2 mv^2 (1/2 x mass x speed^2)
m can be cancelled out because it is on both sides of the equation. This gives:
g x h = 1/2 x v^2
This can be rearranged to find height:
h = 0.5 x v^2 / g
For example, how high must an object be dropped so that it reaches 30 m/s? (g = 10 N/kg)
height = 0.5 x 30^2 / 10
= 45m
