Chapter 12 Work, Energy and Power
Energy Is the ability to do work Expressed in Joules (dzuls) Forms of energy: Mechanical, Heat, light, and Chemical Energy
ENERGY POTENTIAL ENERGY Gravitational potential energy Elastic potential energy KINETIC ENERGY
POTENTIAL ENERGY Gravitational Energy Elastic Potential Energy
Gravitational Potential Energy Is the energy possessed by a body by virtue of its position PE = mgh
Sample Problem 1 A 75.0kg child climbs a 6.00m long slide. What is the potential energy of the child? Given: m = 75.0kg, h = 6.00m, g = 9.8m/s 2 Required: PE = ? Sol’n: PE = mgh = (75kg) (6m) (9.8m/s 2 ) = kg m 2 /s 2 = J
Sample Problem 2 The potential energy of an apple is 6.00 joules. The apple is 3.00-meters high. What is the mass of the apple? Given: h = 3.00m, PE =6.00 J, g = 9.8m/s 2 Required: m = ?
Elastic Potential Energy Is the energy possessed by a spring or rubber band when it is stretched or compressed
Kinetic Energy Is the energy possessed by a body because of its motion KE = ½ mv 2
Sample Problem 3 What is the kinetic energy of a 2,000 kilogram boat moving at 5 m/s? Given: m = 2,000kg, v = 5m/s Required: KE = ? Sol’n:KE = ½ mv 2 = ½ (2000kg) (5m/s) 2 = 1000kg (25m 2 /s 2 ) = 25,000 J
Sample Problem 4 What is the velocity of an 500-kilogram elevator that has 4,000 joules of energy? Given: m = 5,000kg, KE = 4,000 J Required: v = ?
Sample Problem 5 What is the height of a raised object where its mass is 25kg and the potential energy is 34 J?
Sample Problem 6 What is the mass of an object where its velocity is 25m/s and its kinetic energy is J?