# Energy Examples Elastic Examples Chemical Examples Electric In

• Slides: 17

Energy

Examples �Elastic

Examples �Chemical

Examples �Electric

�In this class we will focus on gravitational potential energy and elastic potential energy. �Gravitational Potential Energy is stored energy due to its position above the Earth. �Remember: Energy transferred from one

�Imagine a boulder on a cliff above Wile E. Coyote �The boulder has potential energy due to its position. �It has the potential to fall and do work on him.

PEg = mgh Where: �PEg = Gravitational potential energy (J) �m = mass (kg) �g = acceleration due to gravity (m/s 2) �h = height (m)

Ex. A 15. 0 kg textbook is sitting on a 1. 20 m tall table. If the book is lifted 0. 80 m above the table, how much gravitational potential energy does it have a. with respect to the table? b. with respect to the floor?

�Elastic Potential Energy is energy that is stored in a compressed or a stretched object. �A compressed or a stretched object has the potential to do work when it returns kto its original = spring constant, or a measure of how stiff a shape. spring is. (N/m) �PE =½kx x = distance that the spring has been 2 stretched or compressed

Ex. An archer pulls on a bow string with an average force of 240 N while drawing the arrow back a distance of 0. 200 m. Calculate the potential energy of the bow-arrow system. HINT: The work done to the bow is all being stored as potential energy.

Elastic Potential Energy examples: Textbook p. 166 Q 1 -3 Gravitational Potential Energy examples: Potential energy worksheet

Scalar value Measured in Joules (J) KE = Where: �m = mass �v = speed 2 ½mv

EXAMPLE A 60. 0 kg student is running at a uniform speed of 5. 70 m/s. What is the kinetic energy of the student?

EXAMPLE The kinetic energy of a 2. 1 kg rotten tomato is 1. 00 x 103 J. How fast is it moving?

THE WORK ENERGY THEOREM If a net force acts on an object then it must be accelerating. This acceleration is proportional to its change in kinetic energy. Therefore: W = Fnetd = ∆Ek

EXAMPLE A sprinter exerts a net force of 260 N over a distance of 35 m. What is his change in kinetic energy?

EXAMPLE A student pushes a 25 kg crate which is initially at rest with a force of 160 N over a distance of 15 m. If there is 75 N of friction, what is the final speed of the crate?