Physics - Term 3 - Week 9

Kinetic energy is the energy of an object in motion. It is dependent on the mass of the object and the square of its velocity. The formula for kinetic energy (KE) is KE = 1/2 mv², where m is the mass in kilograms and v is the velocity in meters per second. This means that if the velocity of an object doubles, its kinetic energy increases by a factor of four.

Potential energy is the stored energy of an object due to its position or state. The most common type of potential energy is gravitational potential energy, which is 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.

Consider a car with a mass of 1,000 kg moving at a speed of 20 m/s. To find the 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.

Imagine a rock with a mass of 5 kg placed on a cliff that is 10 meters high. To calculate the gravitational potential energy, we use the formula PE = mgh. Substituting the values, PE = 5 kg * 9.81 m/s² * 10 m = 490.5 J. Therefore, the rock has 490.5 joules of potential energy due to its height.

Let's work through a problem as a class. A bicycle has a mass of 15 kg and is traveling at a speed of 5 m/s. What is its kinetic energy? First, we identify the mass (m = 15 kg) and the velocity (v = 5 m/s). Using the formula KE = 1/2 mv², we calculate KE = 1/2 * 15 kg * (5 m/s)² = 187.5 J. Discuss with your partner how changing the speed would affect the kinetic energy.

Now, let's calculate the potential energy of a 3 kg object at a height of 4 meters. We know the mass (m = 3 kg) and height (h = 4 m). Using PE = mgh, we find PE = 3 kg * 9.81 m/s² * 4 m = 117.72 J. Work with your group to discuss how this energy would change if the height were increased.

Now it's your turn to practice. 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 a 10 kg object at a height of 2 meters. Show your calculations and be prepared to discuss your answers with the class.

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

Answer: KE = 1/2 mv²

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

• A moving car
• A drawn bow
• A rolling ball
• A flowing river

Answer: A drawn bow

A drawn bow stores energy due to its position, making it an example of potential energy.

Answer: Kinetic energy is the energy of an object in motion, dependent on its mass and velocity.

Kinetic energy is defined as the energy possessed by an object due to its motion.

Answer: Joule (J)

Energy is measured in joules (J), which is the standard unit of energy in the International System of Units.

• It doubles
• It triples
• It quadruples
• It remains the same

Answer: It quadruples

Kinetic energy increases with the square of the velocity, so doubling the speed results in quadrupling the kinetic energy.

• Kinetic energy
• Thermal energy
• Potential energy
• Mechanical energy

Answer: Potential energy

Potential energy is the energy stored in an object due to its position, particularly at a height.

Answer: PE = mgh

The formula for gravitational potential energy is PE = mgh, where m is mass, g is the acceleration due to gravity, and h is height.