Week

 Student will: laws of conservation of energy  Demonstrate and apply the laws of conservation of energy in terms of  KineticPotential Energy  Kinetic And Potential Energy

Questions 1)Can an object that has zero height have PE? g is positive because since energy is not a vector, no direction is needed No Trig needed!

Kinetic Energy: Kinetic Energy: Energy due to an object’s motion. KE = ½ mv 2 (J) (kg) (m/s) Kinetic Energy (J) = ½ mass (kg) x (velocity) 2 (m/s) 2)Can an object have both potential an kinetic energy?

Mechanical Energy: Mechanical Energy: Sum of kinetic and potential energy. ME = KE + PE

The law of conservation of energy: The law of conservation of energy: In a closed system, energy cannot be created or destroyed, it can only change forms. PE i + KE i = PE f + KE f mgh i + ½ mv i 2 = mgh f + ½ mv f 2 If friction is involve, that means energy is lost somewhere

Example: Conservation of Energy Gwen Stacy is dropped from 84.3 meters (273.4 ft) from the top of the Brooklyn Bridge. Calculate her velocity right before she hits the water. Assume her mass is 70 kg.

Given: v i = 0 m/s h i = 84.3 m h f = 0 m m = 70 kg a y = g = 9.81 m/s 2 Unknown: v f = ? Steps 1)Define Gwen Stacy is dropped from 84.3 meters (273.4 ft) from the top of the Brooklyn Bridge. Calculate her velocity right before she hits the water. Assume her mass is 70 kg.

Choose an equation or situation: Rearrange the equation to isolate the unknown: 2)Plan Gwen’s potential energy is all converted to kinetic energy

Substitute the values into the equation and solve 3)Calculate

So Gwen Stacy’s final velocity is m/s (Approximately 91 mph) before Spider-Man saves her (and kills her) 4)Evaluate