Work & Energy

Define Work and Energy

Work (measured in Joules) is done when a force that is applied to an object moves that object.
Energy is the ability to do work.

Work is done whenever things are moved or rearranged by a force. A joule is defined as the work expended by a force of one newton through a distance of one metre. To get an object to move, work will need to be done on it.

Define Kinetic Energy

Kinetic energy is the energy a moving object possesses.

Solve Problems Using the Equation for Kinetic Energy

$$E_k=\frac{1}{2}m{v}^2$$

Where $m$ = mass in kg, $v$ is velocity in m/s

1. A 12kg rock is rolling down a hill at 2.0m.s-1. How much kinetic energy does it have?
   E = 1/2mv^2
   E = 0.5*12*2^2
   E = 24J
2. A 7.0kg bowling ball is rolled down an alley at 3.0m.s-1. How much kinetic energy does it have?
   E = 0.5*m*v^2
   E = 0.5*7*3^2
   E = 31.5J
3. What is the mass of a ball which is moving at 4.0m.s-1  and has 32J or kinetic energy
   E = 0.5*m*v^2
   32 = 0.5*m*4^2
   32 = 8m
   m = 4kg
4. What is the velocity of a 3.5kg  ball which has 63J of kinetic energy?
   E = 0.5*m*v^2
   63 = 0.5*3.5*v^2
   36 = v^2
   v = 6m/s

Define Potential Energy

GPE is the energy an object has because of its mass and its position in a gravitational field.
The GPE of an object is a directly proportional to the mass of the object, the height of the object above a reference point and the value of the gravitational field it is in.

Solve Problems Using the Equation for Potential Energy

$$E_p=mgh$$

Where $m$ is mass in kg, $g$ is the strength of gravity in m/s² and $h$ is the height of the object in m.

1. Michael decides to lift his book up into the air.  His book has a mass of 100g and he lifts it 50cm.  Calculate the work done.
   E = mgh
   E = 0.1*9.8*0.5
   E = 0.49J
2. Nancy slams on the brakes on her bike and her brakes do 20,000J of work.  If the combined mass is 100kg what speed was she travelling at?
   E = 0.5mv^2
   20,000 = 0.5*100*v^2
   20,000 = 50*v^2
   V^2 = 400
   V = 20m/s
3. Lucas has a mass of 70kg.  What is his weight on Earth, where the gravitational field strength is 10N/kg?
   W = mg
   W = 70*10
   W = 700N
4. Jakob does some work by pushing a box around with a force of 1N.  He does 5J of work and decides to call it a day.  How far did he push it?
   W = fd
   5 = 1*d
   d = 5m

Conservation of Energy

Define The Law of Conservation of Energy

Use the Law of Conservation of Energy to Account For the Total Energy Involved in Energy Transfers and Transformations With Examples Associated With Sporting Activities and Car Design

Explain Why In Devices That Involve Energy Transfers And Transformations Usable Energy Is Reduced And The System Is Not 100 Efficient

Calculate The Efficiency Of Some Devices That Transform Energy From One Form To Another