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13 Cards in this Set
- Front
- Back
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What is Gravitational Potential Energy (GPE)? |
On Earth we always have the force of gravity acting on us. When we're above the Earth’s surface we have potential (stored) energy. This is called gravitational potential energy (GPE). |
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What two things affect the amount of gravitational potential energy an object on Earth has. |
The objects mass.
The objects height above the ground. |
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What value is the force produced by gravity on a mass of 1 kg? |
The gravitational field at the Earth's surface produces a force of approximately 10N (Newtons) on every mass of 1kg.
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What equation is used to find the gravitational potential energy, GPE, of an object. |
GPE = m x g x h GPE (J) = mass (kg) x gravitational field strength (or 'g') (N/kg) x height (m) |
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What is Kinetic Energy? What is the formula use to calculate Kinetic Energy, Ek? |
Kinetic energy is energy due to movement. Ek = 1/2 mv^2 (^2 = power of 2) Ek = Kinetic Energy in joules (J) m = mass in kilograms (kg) v = speed in metres per second (m/s) |
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Calculate the amount of potential energy that you give a 2 kg ball if you throw it 3 metres upwards. |
GPE = m x g x h = 2 x 10 x 3 = 60 J. |
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Describe the energy transfers that take place when a firework rocket goes off. |
Chemical energy in the gunpowder is transformed into heat that makes gases expand rapidly. Some energy is transferred into sound. The useful energy is transferred into kinetic energy of the rocket. |
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A meteor hits the Earth’s atmosphere at a speed of 50 km/s. If the meteor weighs 40 kg calculate its kinetic energy, and describe what happens to all this energy. |
40 x 50000^2 / 2 50 000 000 000 J (50 000 MJ) The energy is transformed into heat, light (shooting star) and sound. |
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Calculate the extra potential energy the paint tin in the Figure would gain if it was moved from the lower shelf to the higher one. Calculate the kinetic energy of a 5000 kg bus moving at 20 m/s. |
18 J. 1 000 000 J (1 MJ, 1 000 kJ). |
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The Victoria Falls on the Zambezi River in Africa is one of the largest waterfalls in the world. As the water falls, its potential energy must be transferred. Describe what happens to the potential energy. |
The GPE is transferred into KE as the water falls and then into heat and KE of the water in the pool below, which raises the temperature of the water a little. There is also quite a lot of sound energy generated. |
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Calculate the amount of kinetic energy a 30 g mouse would have as it runs at 1.5 m/s across the floor. |
0.033 75 J. |
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If you look closely at the Figure you will note that the last label says it is‘gaining kinetic energy’ as it falls. In fact this kinetic energy is slightly less than the kinetic energy it had when it was thrown upwards. Explain why this is and compare the potential energy with the kinetic energy the ball had at the start and the end of the throw. |
As the ball moves through the air it will encounter air resistance and some of the KE will be transferred to heat rather than GPE. This means that it will have slightly less GPE at the top of its motion than it had KE when it was thrown. The same will happen as it falls again and it will be going slightly less quickly than when it was first thrown and have slightly less KE. |
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What are the key points to remember? |
Gravitational potential energy (GPE) is the energy that an object has due to its position in the Earth’s gravitational field. Change in GPE = mass × gravitational field strength × change in height Ep= m× g× h An object’s kinetic energy depends on its mass and its speed. Ek = ½mv^2 |
