Gravitational Potential & Kinetic Energy Mechanical Energy Gravitational Potential & Kinetic Energy

Gravitational Potential Energy: Note: Same formula as W = Fd Stored energy of a raised object Gravitational Potential Energy (J) Mass of object (kg) Gravity (N/kg)

Ex #1 How much potential energy does a 61.2kg boy have if he is sitting on his bed, 0.5m above the floor? m = 61.2 kg g = 9.8 N/kg ∆h = 0.5 m

Ex #2 A 0.04kg rubber ball drops from a height of 5m to the ground & bounces back to a height of 3m. a) How much potential energy does the ball lose on the trip down? m = 0.04 kg g = 9.8 N/kg ∆h = 5 m b) How much potential energy does the ball regain on the trip back up?

Speed of the object (m/s) Kinetic Energy: Energy of an object due to its motion Result of work having been done to the object Kinetic Energy (J) Speed of the object (m/s) Mass of object (kg)

Ex #3 What is the kinetic energy of a 6kg curling stone sliding at 4m/s? m = 6 kg v = 4m/s

Ex #4 What is the speed of a 5.44kg shotput if its kinetic energy is 68J? m = 5.44 kg Ek = 68J

Ex #5 A 0.5kg rubber ball is thrown into the air. At a height of 20m above the ground, it is traveling at 15m/s. What is the ball’s Ek & Eg? So ball has 154.25J of total energy m = 0.5 kg m = 0.5 kg g = 9.8 N/kg v = 15m/s h = 20 m

BUT….total energy (ET) still the same throughout Eg = high Ek = zero Eg = high Eg = lower Ek = low Ek = higher Eg = higher Ek = lower Eg = zero Ek = high

Total Mechanical Energy (ET): Energy can be transferred or transformed, never lost  Law of Conservation of Energy *If friction negligible If friction is not negligible then….