Le WORK AND ENERGY Show!!!

Work is defined as a force that moves through a distance. The equation used to calculate work is: W=f d If the 60kg cart is moved 20m to the right by a force of 300N, the work done to move the cart this distance is: W=fd W=300N x 20m W= 6000Nm

Here is another situation in which work is done against gravity. Here the cart is pulled or pushed up a hill to a height of 20m. The force being lifted is the weight of the cart. So if we are to determine the work done we must first determine the weight of the cart. Fw = mag Fw = 60kg x 9.80m/s2 Fw = 588N W = fd W= 588N x 20m W=11760Nm

ENERGY is defined as the capacity to do work. There are many forms of energy, but two important forms are Kinetic energy and Potential energy. Kinetic energy is the energy possessed by moving masses. Kinetic energy depends on both the objects mass and the objects velocity. KE= 1/2mv2

The 60kg cart has a velocity of 3.0m/s. The cart’s Kinetic energy is: KE= ½ mv2 KE= ½ 60kg x (3.0m/s)2 KE= 270Nm or 270Joules ( 1 Joule is equal to 1Nm)

Potential energy is energy that is stored and is available for use at some time in the future. There are a number of forms of potential energy…One form is Gravitational Potential Energy. GPE is the energy that is stored by an object because of its position above a surface. Remember the cart that climbed the hill?

The gravitational potential energy stored by the cart when it is at the top of the hill is determined using the equation GPE=mgh GPE=mgh GPE=60kg x 9.80m/s2 x 20m GPE= 11760Joules

Doing work requires energy. In a real sense this means that energy and work are always equal to each other. When work is done moving a force through a distance, energy is consumed. W = fd W= 588N x 20m W=11760Nm Note that the work done and the energy stored are the same. GPE= mgh GPE = 60kg x 9.8m/s2 x 20m GPE = 11760Nm or 11760 Joules

Energy is conserved. This means that energy is never destroyed or lost, it only changes from one form to another. Here is an example of how this happens. When the barrel is rolled to the top of the ramp the GPE stored is: GPE=mgh GPE= 30kg x 9.80m/s2 x 3.0m GPE= 882 J

When the barrel falls off the top of the ramp the GPE is changed into Kinetic energy and then into heat and sound The energy is CONSERVED.

The Law of Conservation of Energy states that energy is conserved. It is never lost or destroyed, it simply changes from one form to another.

Practice what you have learned (A “GPE” problem…) A 2.0kg pendulum swings to a height of 3.0m above its resting position. How GPE does it have at this height? GPE= mgh GPE= 2.0kg 9.8m/s2 3.0m GPE= 58.8J Remember 1Nm = 1Joule

(Another WORK DONE AGAINST GRAVITY problem) A 75kg carpenter climbs to the top of 4.0m ladder. How much work has he done? W=fd W= ( weight) distance This is because his work is done against gravity. W= (m g) d W= (75kg 9.8m/s2) 4.0m W= 2940Nm or 2940J

( A Work / energy theorem problem.) A 75kg carpenter climbs to the top of 4.0m ladder. How much work has he done? GPE=mgh GPE=75kg 9.8m/s2 4.0m GPE= 2940J  ***The answer is the same as the previous problem: Work done = energy gained***

(Work done by a force other than gravity…) • What is the force shown in the diagram below? • F=200N • B. How far did Moe push the Refrigerator? • 10m • C. How much work did he do pushing the refrigerator? • W=fd • W= 200N 10m • W= 2000J

(A kinetic energy problem…) What is the kinetic energy of the .30kg ball shown here? KE=1/2mv2 KE= ½ .30kg (20m/s)2 KE= 60J

The End…for now

Le WORK AND ENERGY Show!!!