P2.2 - Energy
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What is the unit of energy?
Joules (J)
How many joules are there in a kilojoule(kJ)?
1000J
Calculate how far you would need to run to burn off 50g of chocolate using the information given below. On average a person can run 150m per minute. Chocolate has 1500kJ of energy per 100g. 60kJ of energy is burnt off for each minute of running.
50g of chocolate = 1500kJ ÷ 2 = 750kJ Run time = 750 kJ ÷ 60kJ = 12.5mins 12.5mins x 150m = 1875m
State the law of conservation of energy.
Energy cannot be created or destroyed. It can only be transferred.
There are 5 main different types of energy stores. What are they?
Chemical - food, batteries, fuels Gravitational Potential - position in a gravitational field Kinetic - moving objects Elastic - stretching or changing shape Thermal - hot objects
What is meant by a good conductor of energy?
Energy is transferred through it quickly.
What are the three ways that energy can be transferred by.
Conduction Convection Radiation
What is conduction.
Particles transfer energy by colliding with each other when they vibrate.
Are gases good conductors
They are not.
What is a convection current?
Liquid is heated up at a lower section making the particles vibrate. The particles in the liquid move further apart making it less dense. The less dense liquid moves up and the denser colder liquid takes its place.
What does radiation travel as?
Waves.
Does radiation need air to transfer energy?
No. Radiation can be transferred without particles. An example is the sun and how there are no particles in space.
Would a dark blue shirt absorb more or less infrared radiation than a white shirt.
It would absorb more radiation. Dark colours absorb more while light or shiny things would reflect more.
Do animals emit infrared radiation? If so what animals would emit a normal amount and what animals would emit close to none.
Most animals emit infrared radiation including humans. A snake would not emit much infrared radiation as it is cold blooded.
A power rating tells you how much energy is transferred per second. What is the equation to calculate power (W)?
power (W) = energy (J) / time (s)
How do you calculate work done (J)?
work done (J) = force (N) / distance (m)