Physics AQA Topic 1 (Energy changes in a system)

4.11

What is the equation for kinetic energy

KE = (1/2)mv^2

What are the units for the kinetic energy equation

Kinetic energy = J, mass = kg and velocity = m/s

What is the equation for elastic potential energy

∆EPE = (1/2)kx^2 (change in elastic potential energy = 1/2 x spring constant x extension^2)

What are the units for the elastic potential energy equation

Elastic potential energy = J, spring constant = N/m and extension = m

What is the equation for gravitational potential energy

∆GPE = mgh (change in gravitational potential energy = mass x gravitational field strength x height)

What are the units for the gravitational potential energy equation

Gravitational potential energy = J, mass = kg, gravitational field strength = N/kg and height = m

Describe the energy changes involved when an object is projected upwards

Upwards - KE is converted into GPE, peak - maximum GPE so all KE has been converted, downwards - GPE is converted back into KE

What assumption are we making in the flashcard before

We are assuming that there is no air resistance

Describe the energy changes involved when a moving object hits an obstacle

As the object moves towards the obstacle - it has lots of KE, as it collides - KE is transferred into many different types of energy (such as thermal or sound energy) and some of the KE can be transferred to the obstacle, causing it to move

Describe the energy transfers involved when an object is accelerated by a force

Energy is required to accelerate the object (this could be chemical or electrical), which is then converted into KE which is used to accelerate the object

Describe the energy transfers involved when an object is decelerating

The KE of the movement will be transferred to another store of energy (e.g. sound and thermal energy), so the object will have less KE, which slows the object

Describe the energy transfers involved when bringing water to a boil in an electric kettle

Transfer of electrical energy into thermal energy which heats up the kettle, which heats up the water

Describe the energy transfers for a bungee jumper

When falling - the GPE is converted to KE of jumper, as the cord tightens - KE is converted and stored as EPE, at lowest point - the jumper's initial GPE equals the EPE stored in the cord so they do not fall further

Explain why a bungee jumper slows down once the cord begins to stretch

KE decreases since it is converted to EPE - since KE is proportional to (velocity)^2, as KE decreases, so does velocity - making the jumper slow down

What is the equation for change in thermal energy

∆E = mc∆θ (change in thermal energy = mass x specific heat capacity x temperature change)

What are the units for the change in thermal energy equation

Change in thermal energy = J, mass = kg, specific heat capacity = J/kg^C and temperature change = ^C

Define the specific heat capacity of a substance

The amount of energy needed to raise 1kg of a substance by 1^C

What is the definition of power

The rate at which energy is transferred (or rate at which work is done)

State 2 equations for power

P = E/t (power = (energy transferred)/time), P = W/t (power = (work done)/time)

What are the units in the power equations

Energy = J, work done = J, time = s

What is the unit of power

Watt (W)

What is work done

Work done is equal to the energy transferred by an action

How much power is an energy transfer of 1 joule per second equal to

A power of 1 watt

Two motors lift the same mass through the same hight - motor A does this in half the time of motor B - which dissipates the most power

Motor A - the energy transferred is the same but the time taken is less (P = E/t)

Give examples of chemical energy stored

Food, fuel and batteries

State 4 different stores of energy

Kinetic, gravitational potential, elastic potential, and chemical energy