11th Grade ATC Lesson Tuesday Jan. 17, 2012

Instructions Students: Write the notes shown on next slide. Use your notes to write and answer the questions that follow. Don’t forget to turn in your work to your science teacher!

There are two types of energy: In science, energy is a concept that relates to the capacity of matter to perform work as the result of its motion or its position in relation to forces acting on it. There are two types of energy: Kinetic Energy & Potential Energy

Kinetic Energy Energy in motion Derived from the work equation Does not depend on direction Kinetic Energy = ½ x mass x speed² KE = ½mv²

Potential Energy Potential energy is stored energy Two types: Gravitational potential energy Elastic potential energy (to be discussed at a later time)

Gravitational potential energy Depends on object’s mass and height Gravitational potential energy = mass x gravitational acceleration x height GPE = mgh

Questions Three identical balls are thrown from the top of a building, all with the same initial speed. The first ball is thrown horizontally, the second at some angle above the horizontal and the third at some angle below the horizontal. Neglecting air resistance, rank the speed of the balls as they reach the ground, from fastest to slowest. (a)1, 2, 3 (b) 2, 1, 3 (c) 3, 2, 1 (d) All three balls strike the ground at the same speed.

2. Bob, of mass m, drops from a tree limb at the same time that Esther, also of mass m, begins her descent down a frictionless slide. If they both start at the same height above the ground, which of the following is true about their kinetic energies as they reach the ground? (a) Bob’s kinetic energy is greater than Esther’s. (b) Esther’s kinetic energy is greater than Bob’s. (c) They have the same kinetic energy (d) The answer depends on the shape of the slide