Physics - Term 2 - Week 5

Kinetic energy (KE) 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. The faster an object moves, the greater its kinetic energy. For example, a car moving at high speed has significantly more kinetic energy than a stationary car.

Potential energy (PE) 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. An example of potential energy is a book on a shelf; it has potential energy due to its height above the ground.

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 remains constant. For instance, when a ball is thrown into the air, its kinetic energy decreases as it rises, while its potential energy increases. At the peak of its flight, the kinetic energy is at its minimum, and the potential energy is at its maximum.

A car with a mass of 1000 kg is moving 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. Therefore, the rock has 98.1 joules of potential energy.

Let's calculate the kinetic energy of a bicycle with a mass of 15 kg traveling 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. Work through this calculation with your partner and share your results.

Now, calculate the potential energy of a 3 kg object that is 10 meters above the ground. Use the formula PE = mgh. Discuss your findings with your classmates and ensure you understand how height affects potential energy.

Complete the following problems on your own: 1) A 5 kg ball is thrown upwards at a speed of 15 m/s. Calculate its kinetic energy. 2) A 10 kg weight is lifted to a height of 8 meters. Calculate its potential energy. Show all your workings 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.

• Energy of motion
• Energy due to height
• Energy of heat
• Energy of light

Answer: Energy due to height

Potential energy is the energy stored in an object due to its position, often related to height.

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

Kinetic energy is directly related to the mass and velocity 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.

• Zero
• Equal to its potential energy
• Maximum
• Undefined

Answer: Zero

An object at rest has no motion, hence its kinetic energy is zero.

• It increases
• It decreases
• It remains constant
• It becomes kinetic energy

Answer: It decreases

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

Answer: 9 J

Using KE = 1/2 mv², KE = 1/2 * 2 kg * (3 m/s)² = 9 J.

Answer: 235.44 J