Work
Work has a specific physics meaning
Work W=Fd Energy transferred to an object over a distance WORK IS ENERGY GAINED OR LOST W=Fd Where: W – Work (J) F – Magnitude of Force (N) d – distance (m)
Work is scalar (so no direction needed) BUT Force and distance need to be in the same direction
Work Against Gravity To lift an object (at a constant speed), the force applied is equal to the force of gravity If you are lifting up, positive work If you are lowering down, negative work
Example 1 Jacob pushes a shopping cart with a force of 500N through 2.0 m. What is the work done?
Example 1b If the shopping cart has a mass of 40kg and all energy is transferred to kinetic energy, how fast will it be moving after the push?
Example 2 Krinal lifts an object with a mass of 10kg. The object gains 1000J of gravitational potential energy. How high does she lift it? How high could you lift a 10kg mass using all the energy in a piece of gum?
Negative Work Occurs if the force opposes motion In most cases negative work is done by friction – the energy is taken away and turned into thermal energy W=-Fd Where: W – Work (J) F – Magnitude of Force opposing motion (N) d – distance (m)
Example 3 Two students are pushing on a car as shown below. The car moves 10m to the right. How much work does person 1 do? How much work does person 2 do? How much energy is gained by the car?
Work Pg 135 # 1,3,4 Pg 136 # 8-10