Physics - Term 4 - Week 5

Kinetic energy is the energy of an object in motion. It is defined by the formula KE = 1/2 mv², where m is the mass of the object in kilograms and v is its velocity in meters per second. This means that the kinetic energy increases with the square of the velocity, indicating that even small increases in speed can lead to significant increases in kinetic energy.

Potential energy is the stored energy of an object due to its position or state. The most common form is gravitational potential energy, which can be calculated using the formula PE = mgh, where m is the mass in kilograms, g is the acceleration due to gravity (approximately 9.81 m/s²), and h is the height in meters above a reference point. This energy has the potential to be converted into kinetic energy when the object is allowed to move.

Energy can transform from potential to kinetic and vice versa. For example, when a ball is held at a height, it possesses potential energy. Once released, this potential energy converts into kinetic energy as the ball falls. Understanding this transformation is crucial in various applications, such as roller coasters, where potential energy at the top of a hill is converted into kinetic energy as the coaster descends.

A car with a mass of 1000 kg is traveling at a speed of 20 m/s. To find its kinetic energy, we use the formula KE = 1/2 mv². Plugging in the values, KE = 1/2 * 1000 kg * (20 m/s)² = 200,000 J (joules). This means the car has 200,000 joules of kinetic energy.

Consider a rock with a mass of 2 kg that is held 5 meters above the ground. To calculate its potential energy, we use the formula PE = mgh. Substituting the values, PE = 2 kg * 9.81 m/s² * 5 m = 98.1 J. Thus, the rock has 98.1 joules of potential energy.

Let's calculate the kinetic energy of a bicycle with a mass of 15 kg moving at a speed of 10 m/s. Using the formula KE = 1/2 mv², we find KE = 1/2 * 15 kg * (10 m/s)² = 750 J. Discuss with your partner how changes in speed would affect the kinetic energy.

Now, calculate the potential energy of a 3 kg book placed on a shelf 2 meters high. Using PE = mgh, we have PE = 3 kg * 9.81 m/s² * 2 m = 58.86 J. Work with a classmate to explore how moving the book to a higher shelf would change its potential energy.

For homework, calculate the kinetic energy of a soccer ball with a mass of 0.5 kg kicked at a speed of 15 m/s. Then, find the potential energy of the same ball if it is held 1.5 meters above the ground. Be prepared to share your answers in the next class.

• KE = mv
• KE = 1/2 mv²
• KE = mgh
• KE = 2mv

Answer: KE = 1/2 mv²

The correct formula for kinetic energy is KE = 1/2 mv², which shows that kinetic energy depends on mass and the square of velocity.

• Kinetic Energy
• Potential Energy
• Thermal Energy
• Mechanical Energy

Answer: Potential Energy

A raised object possesses potential energy due to its position relative to the ground.

Answer: Kinetic energy is the energy of an object in motion.

Kinetic energy is defined as the energy that an object possesses due to its motion.

• It halves
• It doubles
• It quadruples
• It remains the same

Answer: It quadruples

Kinetic energy increases with the square of the velocity, so if speed doubles, kinetic energy increases by a factor of four.

• 30 J
• 60 J
• 90 J
• 300 J

Answer: 300 J

Using PE = mgh, we calculate PE = 10 kg * 9.81 m/s² * 3 m = 294.3 J, which rounds to 300 J.

Answer: Potential energy decreases as it is converted to kinetic energy.

As an object falls, its height decreases, leading to a decrease in potential energy and an increase in kinetic energy.

• A rock on a cliff
• A moving car
• A stretched rubber band
• A book on a table

Answer: A moving car