Physics - Term 2 - Week 10

Kinetic energy is the energy of an object due to its 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.

The principle of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another. In a closed system, the total energy (kinetic + potential) remains constant. For example, when an object falls, its potential energy decreases while its kinetic energy increases, keeping the total energy unchanged.

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. Therefore, the kinetic energy of the car is 200,000 joules.

Consider a rock with a mass of 5 kg that is held at a height of 10 meters. To calculate its potential energy, we use the formula PE = mgh. Substituting the values, PE = 5 kg * 9.81 m/s² * 10 m = 490.5 J. Thus, the potential energy of the rock is 490.5 joules.

Let's work through a problem together. A bicycle with a mass of 15 kg is moving at a speed of 5 m/s. What is its kinetic energy? Use the formula KE = 1/2 mv². First, calculate v², which is 25 m²/s². Then, KE = 1/2 * 15 kg * 25 m²/s² = 187.5 J. The kinetic energy of the bicycle is 187.5 joules.

Now, let's find the potential energy of a 10 kg object that is 4 meters above the ground. Using PE = mgh, we have PE = 10 kg * 9.81 m/s² * 4 m. Calculating this gives us PE = 392.4 J. Therefore, the potential energy of the object is 392.4 joules.

Now it's your turn! Calculate the kinetic energy of a 25 kg skateboard moving at 3 m/s. Then, calculate the potential energy of a 12 kg object that is 6 meters above the ground. Remember to use the formulas KE = 1/2 mv² and PE = mgh. Show your work and be prepared to discuss your answers.

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

Answer: KE = 1/2 mv²

The correct formula for kinetic energy is KE = 1/2 mv², where m is mass and v is velocity.

• Mass and speed
• Mass and height
• Speed and height
• Mass only

Answer: Mass and height

Potential energy depends on the mass of the object and its height above a reference point.

Answer: Kinetic energy is the energy of an object due to its motion.

Kinetic energy is associated with the movement of an object.

Answer: Energy cannot be created or destroyed, only transformed.

This principle states that the total energy in a closed system remains constant.

• It increases
• It decreases
• It remains the same
• It becomes kinetic energy

Answer: It decreases

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

• Newton
• Joule
• Watt
• Pascal

Answer: Joule

The standard unit of energy in the International System of Units (SI) is the joule.

Answer: 2500 J

Using KE = 1/2 mv², KE = 1/2 * 50 kg * (10 m/s)² = 2500 J.

Answer: 980 J

Using PE = mgh, PE = 20 kg * 9.81 m/s² * 5 m = 980 J.