# Physics - Roller Coasters and Relativity

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• Created by: Elliza
• Created on: 03-06-11 08:52

## Power

WATT IS THE POWER

Power is not the same as force or energy, so something that has a lot of power may not exert a lot of force, it just mostly happens to work that way.

There is a very simple formula to work out power:

Power = Work Done / Time

Example: A motor transfers 4.8 kJ of useful energy in 2 minutes. Find it's power output.

Answer: P = W / t = 4800 / 120  = 40 Q  (or  40 J/s)

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Remember this formula:

POWER = ENERGY TRANSFERRED / TIME TAKEN

1) For running upstairs, the energy transferred is the potential energy you gain.

2) For running, the energy transferred is the kinetic energy you gain (and the potential energy you lose)

For each of these experiments, you must have at least three results and take an average. This ensures reliablilty.

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## Circular Motion

Everything moving in a circle needs a force to ensure it carries on in a circle. The velocity is changing all the time as it is always changing direction.

It is also accelerating, so this must mean it has an overall resultant force.

The force that is acting towards the centre of the circle (keeping it as it is) is called the centripetal force.

The centripetal force could be friction (e.g a car on a road)

It could be tension (e.g a bucket on a rope) or

It could just be gravity pulling it towards the centre (e.g a satellite orbiting Earth)

The faster an object is moving, the bigger the centripetal force has to be. The larger an object is, the bigger the centripetal force has to be. The smaller the circle, the larger the force has to be (to keep it turning).

Continued...

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## Formula for Centripetal Force

• 'F' represents centripetal force
• 'm' represents mass
• 'v' represents speed
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## Roller Coasters

Continued on back...

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## Roller Coasters

At W, the carriage has the most gravitational potential energy.

At X, the potential energy has been converted into kinetic energy, therefore, this is where it has the most kinetic energy, but the least potential energy.

At Y, it has accelerated again, it will have some potential energy.

At Z, it will lose potential energy once again as it will have been converted into kinetic energy

Normally, the carriage will have lost some energy due to air resistance and friction. However, in exams, you can usually leave this out.

All that roller coasters are about is potential energy and kinetic energy... Remember that!

When working out the maximum speed of something on a roller coaster, think of the potential energy it has lost and the kinetic energy it has gained. Just use the formula for kinetic energy.

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