Energy D2: Potential and Kinetic Energy

 FQ:  What things affect the value of KE and PE?

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Kinetic Energy:

Potential Energy

2.  Practice:  Kinetic Energy and Potential Energy Problems

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Mechanical Energy includes gravitational potential energy and kinetic energy.

Kinetic energy is the energy of motion. Moving objects have kinetic energy. 

Gravitational Potential Energy is the energy stored in an object as the result of its vertical position or height. 

Calculating Kinetic Energy

Kinetic energy is calculated using the mass of the object and its speed, or velocity:

KE is the symbol for kinetic energy. It is measured in units called Joules (J) 

m is the symbol for mass. It is measured in units of kilograms (kg)

v is the symbol for velocity. It is measured in units of meters per second (m/s) 

Example: 

What is the kinetic energy of a 1.0 kg car that has a velocity of 1.71 m/s? 

The units "kg" imply that 1.0 is a mass measurement. 

The word "velocity" and the units "m/s" imply that 1.71 is a velocity measurement. 

Plug the values into the formula: 

In a calculator, this would look like:

KE = 1.46 Joules

Calculating Potential Energy

This equation is used to calculate gravitational potential energy:

g, the gravitational acceleration constant, can also be written as g = 9.8 m/s/s

PE is the gravitational potential energy in Joules (J) 

To calculate the gravitational potential energy of an object, multiply mass x 9.8 x height above the ground. 

All formulas are on the Physical Science Reference Tables

Example: 

A cart is pulled at constant speed along a ramp. If the mass of the cart is 3.0 kg and the height at the top of the ramp is 0.45 meters, then what is the potential energy of the cart at the top of the ramp?

The units "kg" imply 3.0 is a mass measurement. 

The units "meters" and the word "height" imply that 0.45 is the height measurement. 

Even though it is not given in the problem, g is ALWAYS equal to 9.8 m/s/s. 

Plug the values into the formula: 

     PE_g = 13.23 J

Practice

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