Work Work has a specific physics meaning Work

Work

• Work has a specific physics meaning

Work • 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 500 N through 2. 0 m. What is the work done?

Example 1 b If the shopping cart has a mass of 40 kg 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 10 kg. The object gains 1000 J of gravitational potential energy. How high does she lift it? How high could you lift a 10 kg 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 10 m to the right. a) How much work does person 1 do? b) How much work does person 2 do? c) How much energy is gained by the car?

Work • Pg 135 # 1, 3, 4 • Pg 136 # 8 -10