Mechanical Energy

Mechanical Energy

By Mr Eko

Kinetic Energy

Work Example

Calculate the kinetic energy stored in a vehicle of mass 1200 kg moving at a speed of 27 m/s.

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What is the Kinetic Energy of a 150 kg object that is moving with a speed of 15 m/s ? .... J

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An object has a kinetic energy of 25 J and a mass of 34 kg , how fast is the object moving? ..... m/s

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An object moving with a speed of 35 m/s and has a kinetic energy of 1500 J, the mass of the object is ..... kg

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What is the Kinetic Energy of a 1200 kg object that is moving with a speed of 24 m/s? ... J

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An object has a kinetic energy of 14 J and a mass of 17 kg , how fast is the object moving? ... m/s

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Gravitational Potential Energy

Worked Question

A man climbs a flight of stairs that is, in total, 3.0 m higher than the floor. The man has a mass of 72 kg, and the gravitational field strength on Earth is approximately 9.8 N/kg. Calculate the energy transferred to the man's gravitational potential energy store.

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A 5 kg cat is lifted 2 m into the air. How much GPE does it gain? ... J

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A large block of stone is held at a height of 15 m having gained 4500 J of GPE. What is it mass .... kg

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A really big beast of a block of stone of weight 600 kg gains 36000 J of GPE. How high has it been raised? .... meter

Mechanical Energy

​When the roller coaster is at rest on top of the hill, it has the maximum potential energy but zero kinetic energy. Because mechanical energy is the sum of both, the value of the potential energy is also the total mechanical energy.

Position 1

​When the roller coaster starts moving downward, it will start to speed up. The process of gaining speed means that kinetic energy is increasing.

This is what transformation of energy looks like. Some potential energy was transformed into kinetic energy when the roller coaster started moving. Adding the amount of potential and kinetic energy at every point in the roller coaster's motion give you the same amount of mechanical energy

Position 2

​The mechanical energy within this system is the same at any point

​Falling Object

Pendulum

Work Example

Multiple Choice

A cyclist travels down a hill from rest at point X, without pedalling. The cyclist applies his brakes and the cycle stops at point Y. Which energy changes have taken place between X and Y?

• gravitational potential → kinetic → thermal (heat)

• gravitational potential → thermal (heat) → kinetic

• kinetic → gravitational potential → thermal (heat)

• kinetic → thermal (heat) → gravitational potential

Multiple Choice

A car is stationary at the top of a hill with the engine switched off. The brakes are released and the car rolls down the hill. At which labelled point does the car have the greatest kinetic energy? Ignore friction

• A

• B

• C

• D

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A heavy object is dropped from a vertical height of 5 m. The speed when it hits the ground is .... m/s

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Pendulum is dropped from position shown. The speed of pendulum bob as it passes through the equilibrium position is .... m/s

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Figure shows a smooth metal block about to slide from B to F. The mass of the block is 0.2 kg and its speed on D is 2.5 m/s. The height of B is .... cm

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