WORK AND POWER Work when a force is

WORK AND POWER

Work- when a force is applied over a distance in the direction of the motion. Scalar quantity Work = Force x distance W = Fd Unit: Nm or Joule (J)

Ex 1: A 40 kg cart is rolled along the floor by a horizontal force at a constant velocity. If 150 N is applied to the cart for 10 m, how much work is done? F = 150 N W = Fd W = 150 N( 10 m) W= 1500 J

Ex 2: A sailor pulls a boat along a dock for 30 m with a force of 250 N. What work is done if the rope is held at 60° with respect to the water? Fp = F cosѲ Fp = 250 N cos 60° Fp = 125 N 60° Fp W = Fp d W= 125 N(30 m) W= 3750 J

SIMPLE MACHINES a) Redirects the applied force b) Breaks job up into smaller repetitions Levers Pulleys Gears wedge wheel and axel

Work output - Work done by a machine. Work input -work done to operate the machine. %Efficiency = Work output x 100 Work input Ex: A pulley system lifts a 90 N crate 3 m up. If a man applies 30 N of force for a length of 15 m, what is the efficiency of the pulley system? %E = (90 N)(3 m) x 100 = 60% efficient (30 N)(15 m) Where did the other 40% go?

POWER- The rate of doing work Power = Work time P= W/t = (Fd)/t = Fv Unit: J/s or watt (W) *English unit= horse power (746 watts)*

Ex: A machine produces a force of 40 N over a distance of 100 m. If it does this in 5. 0 seconds, what is the power of the machine in watts and kilowatts? P = Fd/t P = 40 N( 100 m) 5. 0 sec P= 800 W P = 0. 80 k. W