Work & Power QOD: List and explain an example of work & power relevant to your life.
Work Is done when a force is applied to an object in the same direction that the object moves This means that work is ONLY done if the object moves in the direction of the force
Equation for Work Work = Force(F) X Distance (d) W = Fd Work is measured in Joules(J)
1. Annie’s sister Sally refuses to move from in front of the TV 1. Annie’s sister Sally refuses to move from in front of the TV. Annie applies a force of 500N and pushes Sally 1.5m. How much work did Annie do? W = Fd F = 500 N d = 1.5 m W = (500 N) ( 1.5 m) W = ? W = 750 J
2. Andrew hits a baseball 100m 2. Andrew hits a baseball 100m. If he used 1000J of energy to hit the ball, how much Force did he apply? d = 100 m W = Fd W = 1000 J F = W / d F = ? F = 1000 J / 100 m F = 10 N
W = (2600N)(15m) W = Fd m = 1300kg W = 39000 J Vi = 10m/s Vf = 20m/s 3. You are in your car for the first time by yourself. You accelerate your 1300 kg car from 10 m/s to 20 m/s in 5s. Just as you reach 20m/s, you slam into the car in front of you and push that car 15m. How much work do you do on the car in front of you? W = (2600N)(15m) W = Fd m = 1300kg W = 39000 J Vi = 10m/s Vf = 20m/s F = ma F = (1300kg)(2m/s2) t = 5s F = 2600 N a = (vf – vi) / t d = 15m W = ? a = (20m/s – 10m/s) / 5s a = 2m/s2
Power Is how much work is done in a given amount of time The faster you do work, the more power you have to use.
Power Equation Power = Work / time P = W / t Power is measured in Watts(W) 746 Watts equals 1 horsepower(hp)
4. Your family is moving to a new apartment. While lifting a box 1 4. Your family is moving to a new apartment. While lifting a box 1.5m straight up to put it on a truck, you exert an upward force of 200N for 1.0s. How much power is required to do this? P = (300J) / 1s P = W / t d = 1.5m P = 300 W F = 200N W = Fd t = 1s W = (200N)(1.5m) P = ? W = 300 J
5. You lift a book from the floor to a bookshelf 1.0m above the ground. How much power is used if the upward force is 15.0N and you do the work in 2.0s? d = 1 m P = W / t P = (15J) / 2s P = ? P = 7.5 W F = 15 N W = Fd t = 2 s W = (15N)(1m) W = 15 J
6. You apply a horizontal force of 10 6. You apply a horizontal force of 10.0N to pull a wheeled suitcase at a constant speed of 0.5m/s across flat ground. How much power is used? (Hint: use the time given to you in the units) P = (5J) / 1s P = W / t F = 10 N P = 5 W s = 0.5 m/s W = Fd P = ? W = (10N)(0.5m) d = 0.5 m t = 1 s W = 5 J