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Mechanical Energy. Gravitational Potential Energy. The energy possessed by an object because of its position relative to a lower position The potential of an object to be pulled down by gravity. A GPE Machine. E g = mgh Eg – gravitational potential energy (J) m – mass (kg) - PowerPoint PPT Presentation
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Mechanical Energy
Gravitational Potential Energy
•The energy possessed by an object because of its position relative to a lower position
•The potential of an object to be pulled down by gravity
A GPE Machine
Eg = mghEg – gravitational
potential energy (J)m – mass (kg)g – gravitational field strength (N/kg or m/s2)h – height above reference
level (m)
•We always have to indicate a reference level
Ex. The gravitational potential energy is 30J relative to the Earth’s surface
Sample Problem:
A 58 kg skydiver stands in the door of a plane preparing to jump. If the earth is 2.8 km below the skydiver, what is the skydiver’s potential energy relative to the earth?
Kinetic Energy
•the energy possessed by an object due to its motion
Calculating Kinetic Energy:
Ek = ½ mv2
Ek – Kinetic Energy (J)
m – mass (kg)v – Speed (m/s)
Sample Problem:
What is the kinetic energy of a 60 g tennis ball that has a speed of 3.6 m/s?
Mechanical Energy
•The sum of the gravitational potential energy and the kinetic energy
•Think of TOTAL energy of an object due to it’s motion/position
•Mechanical energy will always stay the same unless WORK is done
•Ex. When a parachutist jumps from a plane, she initially has a large GPE and no kinetic energy. As she falls, she speeds up as her GPE converts to kinetic energy
Her Mechanical Energy will always be the same
Calculating Mechanical Energy
Em = Eg + Ek
Ek – Kinetic Energy (J)Eg – Gravitational Potential
Energy (J)Em – Mechanical Energy (J)
Applications of Mechanical Energy•South African vultures eats bones – if they are too big the bird will drop them from a greater height so they break
Applications of Mechanical Energy•A roller coaster on a track – the height of
the first hill has to be high enough giving a high potential energy – this will be converted into kinetic energy which will make it go really fast
•A roller coaster on a track – the height has to be high enough to create enough potential energy – this will be converted into kinetic energy which will allow the cart to get around the track•A roller coaster on a track – the height has to be high enough to create enough potential energy – this will be converted into kinetic energy which will allow the cart to get around the track
Top Thrill Dragster – Cedar Point, Ohio
•128 m tall, 193 km/h on the up and down
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