Energy, Work, and Power

Some Definitions

Work= Force X Distance

If a person exerts 20 Newtons of force to move 5 meters, he has done 100 Joules of work.

W= 20N X 5m = 100 J

Solve this Problem:

A ball weighing three Newtons falls a distance of 4 meters. What work has been done?

Work Done?

a. A teacher applies a force to a wall and becomes exhausted. Explanation:________________________________________________________________________

Yes or No

b. A weightlifter lifts a barbell over her head. Explanation:________________________________________________________________________

Yes or No

c. A waiter carries a tray full of meals across the dining room at a constant speed. Explanation:________________________________________________________________________

Yes or No

d. A rolling marble down hits a note card and moves it across a table. Explanation:________________________________________________________________________

Yes of No

e. A shot-putter launches the shot. Explanation:________________________________________________________________________

Yes or No

Let's Practice!

Tap the ball to reveal the assignment

Mechanical Advantage and Mechanical Efficiency

Both ratios (fractions and percentages) show us how well the machine works.

Mechanical Efficiency--How well the machine uses the energy you put into it. It compares the work you do to the machine and the work you get out. The work you get out of the machine is always less than the work you put in and you lose some energy to friction.

ME= work outputwork input

X 100

Mechanical Advantage--How much force you get out of the machine. Your mechanical advantage should be greater than 1 for the machine to be useful.

MA = Force outputForce input

Attachments

Practice Problems on Work.docx