Physics - Term 4 - Week 8

The law of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another. This principle is fundamental in physics and applies to all physical processes. For example, when a ball is thrown into the air, its kinetic energy is converted into potential energy as it rises, and then back into kinetic energy as it falls.

Consider a pendulum. At its highest point, the pendulum has maximum potential energy and minimal kinetic energy. As it swings down, potential energy is converted into kinetic energy. At the lowest point, the kinetic energy is at its maximum while potential energy is at its minimum. This continuous transformation illustrates the conservation of energy in action.

Let's work through a problem together. A 2 kg object is lifted to a height of 5 meters. Calculate the potential energy gained by the object. Use the formula PE = mgh, where m is mass, g is the acceleration due to gravity (9.8 m/s²), and h is height. The potential energy is PE = 2 kg * 9.8 m/s² * 5 m = 98 J. Discuss how this energy would change if the object were dropped.

Now, solve the following problems on your own. 1) A 1.5 kg ball is dropped from a height of 10 m. Calculate its potential energy at the top and its kinetic energy just before it hits the ground. 2) A car with a mass of 1000 kg is moving at a speed of 20 m/s. Calculate its kinetic energy. Remember to use the formulas for potential energy (PE = mgh) and kinetic energy (KE = 0.5mv²).

• Energy can be created and destroyed.
• Energy can only be transformed.
• Energy is always lost in transformations.
• Energy can be created from matter.

Answer: Energy can only be transformed.

The law states that energy cannot be created or destroyed, only changed from one form to another.

• A stretched spring
• A moving car
• A book on a shelf
• A charged battery

Answer: A moving car.

Kinetic energy is the energy of motion, and a moving car exemplifies this.

Answer: Potential energy is the energy stored in an object due to its position or configuration.

It is energy that has the potential to do work based on the object's position, such as height above the ground.

• It increases.
• It decreases.
• It remains constant.
• It is converted to thermal energy.

Answer: It decreases.

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

Answer: KE = 0.5mv².

Kinetic energy is calculated using the mass of the object and its velocity.

• 19.6 J
• 98 J
• 20 J
• 39.2 J

Answer: 196 J

Potential energy is calculated as PE = mgh = 10 kg * 9.8 m/s² * 2 m = 196 J.

• Thermal energy
• Chemical energy
• Nuclear energy
• Time