Energy and Power

Energy and Power

by Walid Hafizul

7.1 Work, Energy and Power

7.2 Potential Energy and Kinetic Energy

7.3 Principle of Conservation of Energy​

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​Work

​product of force and displacement in the direction of the force

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W = Fs

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​unit: Joule (J)

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​Energy

​Ability to do work

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​unit: Joule (J)

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Power

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what is the formula to find work done?

​work is done

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What is the work done by the man if he pushes the stroller with 15 N for 5 m?

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How much force is applied if this rowing team put 54 kJ work done and it took 30 m to the finish line?

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How far does this man can cycle if the work done is 81 kJ with a consistance 60 N force applied?

Poll

any work done here?

• Yes

• No

Poll

Andrew and Matthew carry an identical sack of apples from the garden to the playground. If Matthew reach the destination before Andrew, who has more power?

• Andrew

• Matthew

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A 20 N toy car move 3 m in a straight line for 2 seconds. What is the power used 

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how long will it takes for a man to reach the finish line on a 100 m sprint if he put 500 J energy?

His weight is 500 N

7.2​ Potential Energy and Kinetic Energy

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​Gravitational Potential Energy

​work done to lift an object to a height, h from the Earth's surface

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​E_g = mgh

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​m: mass (kg)

​g: gravitational acceleration (ms^-2)

​h: height (m)

​Work done and Gravitational Potential Energy

​w = Fs

​F is vertically upward, known as Weight

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​w = weight x s

​weight is mg

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​w = mgs

​s is height lifter, h

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​w = mg

Poll

is there any gravitational potential energy on the apples

• Yes

• No

• Doubt

• Prefer not to say

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image shows fish hanging 2 meters from the surface on a pole. Calculate the gravitational potential energy if the fish has a mass  3 kg?

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image shows fish hanging 2 meters from the surface on a pole. Calculate the mass of the fish if it has 100 J gravitational potential energy?

Elastic Potential Energy

​Work done and Elastic Potential Energy

Elastic potential energy = area under the graph

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If the sling shoot pulled 25 cm with 7 N force. Calculate the elastic potential energy possessed by the sling shoot

Multiple Choice

What kind of energy is stored in the object?

• Gravitational potential energy

• Elastic potential energy

• Kinetic energy

Multiple Choice

What kind of energy is stored in the object?

• Gravitational potential energy

• Elastic potential energy

• Kinetic energy

Multiple Choice

What kind of energy is stored in the object?

• Gravitational potential energy

• Elastic potential energy

• Kinetic energy

​Kinetic Energy

Open Ended

Name something that has kinetic energy

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When a car of mass 200 kg moves with a velocity of 180 kmh^-1. How much kinetic energy is possessed by the car?

7.3 Principle of Conservation of Energy​

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​Principle of Conservation of Energy

​Energy cannot be created or destroyed but can only be converted from one to another.

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The length of the string pulled 0.8 m. If a force of 5 N used to pull the string, calculate the maximum speed of the arrow of mass 60 g.

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A crane raised a load to a height of 8 m in 5 seconds. What is the power supplied by the crane to raise the load which has a mass of 400 kg?

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A crane raised a load to a height of 8 m in 5 seconds. The load has a mass of 400 kg.

After raising the cement to a height of 12 m, the cable snaps. What is the kinetic energy of the cement the moment it reaches the floor?