Kinetic Energy

Kinetic Energy

High School

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Learning Objectives

Key Vocabulary

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Energy

The capacity to do work or the ability to cause change in a physical system.

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Kinetic Energy

The energy an object possesses due to its motion, dependent on its mass and speed.

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Joule

The standard international (SI) unit of measurement for energy and work, abbreviated as J.

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Work

The measure of energy transfer that occurs when an object is moved by an external force.

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Scalar

A physical quantity that is fully described by its magnitude or numerical value alone.

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What is Kinetic Energy?

• Kinetic energy is the energy an object has because of its motion.

• It depends on the object's mass and its velocity, or speed.

• More mass or velocity means the object has more kinetic energy.

• An object at rest has zero kinetic energy since it is not moving.

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Solved Example 1
A 6 kg bowling ball is rolling down the lane at a speed of 7 m/s. What is the kinetic energy of the bowling ball?

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
A 6 kg bowling ball is rolling down the lane at a speed of 7 m/s. What is the kinetic energy of the bowling ball?

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Step 2: Solve for the Unknown

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Solved Example 1
A 6 kg bowling ball is rolling down the lane at a speed of 7 m/s. What is the kinetic energy of the bowling ball?

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Step 3: Evaluate the Answer

• The calculation is done correctly. Squaring the velocity first is important.

• The final unit is Joules, which is correct for energy. The answer is positive, which is expected for kinetic energy.

Multiple Choice

Which statement accurately describes the conditions for an object to have kinetic energy?

• The object must have a positive charge.

• The object must have force and acceleration.

• The object must be stationary.

• The object must have mass and be in motion.

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Calculating Kinetic Energy

Multiple Choice

An object has a mass of 10 kg and is moving at a velocity of 3 m/s. What is its kinetic energy? The formula for kinetic energy is  $$KE = \frac{1}{2}mv^2$$ .

• 90 J

• 15 J

• 30 J

• 45 J

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What is the Work-Energy Theorem?

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Solved Example 3
A 1,500 kg car accelerates from 10 m/s to 25 m/s. Calculate the work done on the car during this acceleration.

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Step 1: Analyze and Sketch the Problem

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Solved Example 3
A 1,500 kg car accelerates from 10 m/s to 25 m/s. Calculate the work done on the car during this acceleration.

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Step 2: Solve for the Unknown

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Solved Example 3
A 1,500 kg car accelerates from 10 m/s to 25 m/s. Calculate the work done on the car during this acceleration.

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Step 3: Evaluate the Answer

• The car sped up, so its kinetic energy increased, which means positive work was done on it. Our answer, 393,750 J, is a positive value, which is consistent.

• The unit for work and energy is Joules (J), which is correctly used in the answer.

Multiple Choice

If the work done on a moving object is positive, what is the resulting change in its kinetic energy?

• The kinetic energy becomes zero.

• The kinetic energy increases.

• The kinetic energy remains the same.

• The kinetic energy decreases.

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Common Misconceptions About Energy

Misconception	Correction
Energy always involves visible motion.	Energy can be stored without any visible movement, as in chemical or potential energy.
Kinetic energy can be a negative value.	Kinetic energy is always positive or zero, as mass and velocity squared are non-negative.
Doubling mass and velocity have the same effect on kinetic energy.	Doubling velocity quadruples kinetic energy, while doubling mass only doubles it.

Multiple Choice

A cyclist and their bike have a combined mass of 80 kg and a kinetic energy of 1,600 J. If the mass is doubled to 160 kg while the velocity stays the same, what is the new kinetic energy?

• 1,600 J

• 800 J

• 6,400 J

• 3,200 J

Multiple Choice

Which statement correctly explains why kinetic energy is a scalar quantity?

• It can be a positive or negative value.

• It is calculated using velocity, which is also a scalar.

• It has a specific magnitude but no associated direction.

• It has a direction but no specific magnitude.

Multiple Choice

A 2,000 kg car is at rest. Brakes fail and it rolls down a hill, reaching a velocity of 15 m/s. What is the work done on the car by gravity? (Hint: $$W = \Delta KE$$ )

• 30,000 J

• 225,000 J

• 15,000 J

• 450,000 J

Multiple Choice

Which of these two changes would cause a greater increase in an object's kinetic energy: doubling its mass or doubling its velocity?

• Doubling its velocity.

• The effect depends on the initial velocity.

• Doubling its mass.

• Both changes would have the same effect.

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Summary

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

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• 3

• 4