Work, force, motion, and power 12/14 - 12/16 Using mathematical formulas Solving word problems

Learning Objectives: Students will be able to 1 Learning Objectives: Students will be able to 1. recognize units of measure and correctly apply them to mathematical problems 2. apply mathematical equations to describe the relationships between force, work, and power

Force, Work, Power A force is a push or a pull Work is a force acting over a certain distance Power how quickly work is done

PROBLEM 1 (sample) How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Given (know): Need to know: Formula: Substitute: Compute: Final Answer:

Know (Given): Force = 30 Newtons Distance = 3 meters Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Know (Given): Force = 30 Newtons Distance = 3 meters

Need to know: Work = ? Joules Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Need to know: Work = ? Joules

Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Formula Needed: Work = Force x Distance

_____ Joules = 30 Newtons x 3 meters Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Substitute: _____ Joules = 30 Newtons x 3 meters

Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Compute: 30 x 3 = 90

Final Answer: Work = 90 Joules Sample PROBLEM How much work is done by a person who uses a force of 30 Newtons to move a grocery cart 3 meters? Final Answer: Work = 90 Joules

Problem Solving Process Given: Force = 30 Newtons Distance = 3 meters Need to Know: Work = ? Joules Formula: Work = Force x Distance Substitute ?J = 30N x 3m Compute 30 x 3 = 90 Final Answer: Work = 90 Joules

Problem 2a: How much work is done by a person who uses a force of 40N to move a grocery cart 4 meters? Need to know: Formula: Substitute: Compute: Final Answer:

problem 2b. How much work is done if the person pushes with the same force (40N), but the grocery cart moves 0 meters? Know: Need to know: Formula: Substitute: Compute: Final Answer:

Problem 3 5000 J of work is done to lift a rock 50 meters. How much force is applied? Know: Need to know: Formula: Substitute: Compute: Final Answer: By lifting this rock you are increasing its _________________ energy.

Problem 4 A teacher does 200 joules of work in 10 seconds. How much power did he use? Know: Need to know: Formula: Substitute: Compute: Final Answer: He could have increased power by increasing the amount of ________________ or decreasing the amount of ______________.

Problem 5 (Page 78, Question 3) How much power, in watts, is needed to cut a lawn in 50 minutes if the work involved is 100,000 Joules? (* Must convert _____________ to ______________) Know: Need to know: Formula: Substitute: Compute: Final Answer:

Problem Solving Process Given: Time = 50 minutes Work = 100,000 Joules Need to Know: Power = ? Watts Formula: Power = Work/Time Substitute: 100,000 J / 50 minutes = ? Watts Compute: 50 minutes x 60 seconds/1 minute = 3000 seconds 100,000/3,000 = 34 Final Answer: Power = 34 Watts

More Practice: Page 78 # 1-7 Page 96 #11,12,13 Page 98 # 1,7,9