Work and Inclined Planes Work Review W = Fd Example: How much work is done in the picture below? 30 N 10 m Answer: 300J Going Straight Up How much work is done lifting the small box to the top of the tower. ● 12 m 5 kg Solution The force is g. So W = mgh W = 5 * 9.8 * 12 W = 588J Going Down a Slide Find the amount of work done. ● 5 kg 6m 30° Solution (Hard Way) Find the distance h = d sinθ d= h sinθ Find the Force F = mg sin θ W = Fd = mg sin θ * h sin θ W = mgh Which Brings us to the Easy Way Just use mgh, and you will have a direct route to the answer. Answer: 25 * 9.8 * 3.0 = 735 J Going up a Ramp Which takes more work, lifting an object straight up, or pushing an object up a ramp? 5m 5m 5 kg 5 kg 30 ° Answer Part I Let’s calculate lifting an object straight up: W = mgh W = 5 * 9.8 * 5 W = 245 J Answer Part II Going up a ramp: W = Fd F = mg sin θ d = h/sin θ Multiply and the sin’s cancel. We get W = mgh, which is what we had before Practice Roger is loading a truck. The bed of the truck is .75 m off the ground. If he lifts a 75kg chair into the truck, how much work has he done? Solution: W = mgh W = .75 * 9.8 * 75 W = 551.25 J In Conclusion Bear in mind This is without friction With friction things get a lot more messy But that’s a different workshop. The End