1. Mechanical Energy mechanical energy = gravitational potential energy + kinetic energy kinetic energy energy an object has due to motion gravitational potential energy energy an object has due to it’s position above a reference level Rollercoaster Energy

2. Gravitational Potential Energy We must do a certain amount of work to raise an object above the Earth’s surface. Therefore, once the object is raised it will possess a certain amount of potential energy. To determine the amount of potential energy an object has when it is raised use: W = F  d(F=mg) = mg  d = mg  h W = E g  E g = mg  h E g = gravitational potential energy (J) m = mass of object (kg) g = gravitational constant (9.8 N/kg)  h = vertical displacement of object (m)

3. 1. A student raises a 25.0kg box from the floor to a counter 98.0cm above the floor. Calculate it’s gravitational p.e. m = 25.0 kg g = 9.81 N/kg h = 0.98 m E g = ? E g = mg∆h = (25)(9.81)(0.98) = 240.35 J The gravitational p.e. is 240 J. 4.3 Prac. #1, 4-6

4. Kinetic Energy Kinetic energy is the energy of a moving object and is affected by two factors: 1.mass of the object 2.speed of the object To determine an object’s kinetic energy use: E k = ½ mv 2 E k = kinetic energy (J) m = mass of object (kg) v = final speed of the object (m/s)

5. 2. What is the kinetic energy of a 7.3kg rock moving at 30.0m/s? m = 7.3 kg v = 30.0 m/s E k = ? E k = ½ mv 2 = (0.5)(7.3)(30) 2 = 3285 The kinetic energy of the moving rock is 3285 J. 4.3 Prac. #8, 11, 12 UC #2-7