3 A: Definition of WorkWork: The product of force and distance when a force is used to move an object.
4 B: No Work Without Motion! In order for you to do work on an object, the object must move some distance as a result of your force.
5 C. Only Force in the Same Direction In order to do work on an object, the force you exert must be in the same direction as the object’s motion.
6 Is it work? #1. Pulling books out of your backpack. #2. Carrying a bag of groceries.MotionLiftMotionLiftForce applied: lifting bagsForce applied: lifting (pulling) booksDistance: bags move, but different direction than the forceDistance moved: distance from bag to table.
11 G. Practice Problems#1. To help rearrange the furniture in your classroom, you exert a force of 20 N to push a desk 10 m. How much work did you do?Work = Force X DistanceWWork = 20 N X 10 mFDWork = 200 J
12 #2. A hydraulic lift exerts a force of 12,000N to lift a car 2 m #2. A hydraulic lift exerts a force of 12,000N to lift a car 2 m. How much work is done on the car?Work = Force X DistanceWork = 12,000 N X 2 mWork = 24,000 JWFD
13 #3. It took 500 Joules to push a chair 10 meters across the floor #3. It took 500 Joules to push a chair 10 meters across the floor. With what force was the chair pushed?Force = WorkDistanceForce = 500 J10 mForce = 50 NWFD
21 Practice Problems#1. A crane lifts an 8,000 N beam 75 m to the top of a building in 30 seconds. How much power does the crane use?Power = WorkTimeWork = Force X DistanceWork = 8,000 N X 75 mPower = 600,000 J30 sWork = 600,000 JPower = 20,000 WWFDWPTWork TrianglePower Triangle
22 Practice Problems#2. A motor exerts a force of 10,000 N to lift an elevator 6 m in 5 seconds. What is the power produced by the motor?Power = WorkTimeWork = Force X DistanceWork = 10,000 N X 6 mPower = 60,000 J5 sWork = 60,000 JPower = 12,000 WWFDWPTWork TrianglePower Triangle
23 Practice Problems#3. A tow truck exerts a force of 9,000 N to pull a car out of a ditch. It moves the car a distance of 6 m in 25 s. What is the power of the tow truck?Power = WorkTimeWork = Force X DistanceWork = 9,000 N X 6 mPower = 54,000 J25 sWork = 54,000 JPower = 2,160 WWFDWPTWork TrianglePower Triangle
28 B. Two Types of Energya. Kinetic Energy- the energy an object has due to its motion.Example: a rolling ball.b. Potential Energy- energy that is stored in an object due to its position.Example: a bow and arrow.Example: a battery.
29 Identify one form of potential energy and one form of kinetic energy.
30 C. Calculating Energy Kinetic Energy = b. Units – mass= kilograms (kg) Mass X Velocity22K.E. = mv22b. Units –mass= kilograms (kg)velocity = meters per second (m/s)K.E. = Joules
31 c. Practice Problems i. An 80 kg man is jogging at a velocity of 4 m/s. What is his kinetic energy?K.E. = mv22K.E. = 80 kg X (4 m/s)22K.E. = 80 kg X 16 m/s2K.E. = 640 J
32 ii. A 40 kg boy is jogging at a velocity of 4 m/s. What is his kinetic energy?K.E. = mv22K.E. = 40 kg X (4 m/s)22K.E. = 40 kg X 16 m/s2K.E. = 320 J
33 iii. A 40 kg boy is jogging at a velocity of 2 m/s. What is his kineticenergy?K.E. = mv22K.E. = 40 kg X (2 m/s)22K.E. = 40 kg X 4 m/s2K.E. = 80 J