3A: Definition of WorkWork: The product of force and distance when a force is used to move an object.
4B: 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.
5C. 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.
6Is 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.
11G. 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
21Practice 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
22Practice 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
23Practice 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
28B. 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.
29Identify one form of potential energy and one form of kinetic energy.
30C. 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
31c. 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
32ii. 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
33iii. 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