1. Wednesday, 12/10/14PHYSICS If you do the same old things, you get the same old results!

2. Wednesday 12/10/14 PHYSICS ex. 1

3. Work, Energy, Power, and Momentum defn. Work (W) – work done by a force is the product of the displacement and the component of the force in the direction of the displacement. NOTE: Work is a SCALAR quantity! UNITS: 1Nm = 1 J (joule) To get joules, you must use kg, m, and s. (Usually, just W = Fdcos θ.) Wednesday 12/10/14 PHYSICS

4. ex. 2 A 5.0kg crate is dragged 10.0m across a floor by a 12N force applied at 30.0º above horizontal. a) Find the work done by the force. b) If a constant frictional force of 8.4N exists, find the work done by friction. θ is the angle between the force and the displacement!!! Forces that are perpendicular to displacement do NO work (cos 90 = 0)!!

5. ex. 3 How much work must a person do to lift a 49kg crate a distance of 10.0m straight up at constant speed? defn. power (P) – the rate at which work is done P = W/t P – power W – work t – time UNITS: J/s = W (watts) sometimes horsepower (hp) 1 hp = 746W

6. ex. 4 p. 181 #5 1500kg car accelerates uniformly from rest to 10.0m/s in 3.00s. a) What is the (net) work done on the car in this time interval? b) What is the (net) power delivered in this time interval. HW 26: ws. 2, 7 – 15 odd

7. HW 24 7) 6300J 9) 60° 11) a) 715N b) 10,000J Thursday, 11/29/12 ex. 1 ex. 2 A 5.0kg crate is dragged 10.0m across a floor by a 12N force applied at 30.0º above horizontal. a) Find the work done by the force. b) If a constant frictional force of 8.4N exists, find the work done by friction. ex. 3 How much work must a person do to lift a 49kg crate a distance of 10.0m straight up at constant speed? ex. 4 p. 181 #5 1500kg car accelerates uniformly from rest to 10.0m/s in 3.00s. a) What is the (net) work done on the car in this time interval? b) What is the (net) power delivered in this time interval.

8. HW 26 HW 24 7) 6300J 9) 60° 11) a) 715N b) 10,000J HW 26 HW 24 7) 6300J 9) 60° 11) a) 715N b) 10,000J