17 Conservation of Energy Energy can neither be created nor destroyed. It can only change from form to form.Mechanical Energy, PE and KEConservation of Mechanical EnergyPE1 + KE1 = PE2 + KE2
18 What happens when friction is present? When friction is present, the work done by the frictional force W=fd is transferred to heat energy.Friction is a “non-conservative” force.
19 A Force is “Non-Conservative” if: “the work it does on an object that moves between two points depends on the path taken.”“the work it does on an object that moves through a round trip is non-zero.”Example: friction, tension, normal force, propulsion forces.
20 A Force is “Conservative” if: “ the work it does on an object that moves between two points depends only on the position of these two points and not on the path.”“the work it does on an object that moves through a round trip is zero.”Example: gravity, force of a spring.
21 Problem 5 A 3kg watermelon sits on a table 1.2m above the ground. What is its PE at the top compared to the ground?b) What is its KE at the top?c) With what speed will it hit the ground? A: 36J, 0J, 4.9m/s
22 Problem 6A penny is at the top of the Empire State Building 381m above the ground. It is then released. With what speed will it hit the ground?A: 87.3 m/s
23 Problem 7-Roller Coaster A roller coaster car started from point A at a height of 100m. What is its speed at point B? A: 44.7m/s
24 Problem 8 - Penduluma) What is the potential energy of the bob at point A compared to the ground? b) What is the speed of the bob at the bottom? A: 2.3J, 1.1m/sA