3.2.1 Intro to Work and Energy

3.2.1 Intro to Work and Energy

​•energy:  ABILITY TO DO WORK

–Unit:  JOULE (J)

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•work:  A CHANGE IN TOTAL ENERGY

–requires MOTION

–Unit: JOULE (J)

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Multiple Choice

Example 1: No Motion

•A student is trying to push a heavy crate across the floor, but it does not move. 

–Is work being done ‘on the crate’?

• Yes, the student is applying force so there is work done on the box

• No, work is NOT being done on the box unless it moved

• Not enough information to determine

• Bigfoot strikes again!

​Example 1: No Motion

​•But it feels to the student like energy is being used -- what’s going on?

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​Energy IS being expended and work IS being done, just not ‘on the object’.  Work is being done inside the student’s body.

Multiple Choice

​Example 2: A box is pushed with a force of 100 newtons across a frictionless surface for a distance of 10 meters. 

–How much work is done on the box?

• 1.02 J

• 102 J

• 1000 J

• 0 J

​Example #4 – Force on an Angle

​•A sled is pulled a horizontal distance of 4.0 meters across a frictionless surface using a force of 15 newtons at an angle of 30° above the horizontal. 

–How much work is done on the sled?

Multiple Choice

​Example 4: A sled is pulled a horizontal distance of 4.0 meters across a frictionless surface using a force of 15 newtons at an angle of 30° above the horizontal. 

–How much work is done on the sled?

• 52 J

• 60 J

• 30 J

• 3.25 J

Multiple Choice

•A 300N for is required to hold a 50N box in place on a 5m long ramp at an incline of 25 degrees. How much work is done by holding the box in place?

• 0N

• 250N

• 1500N

• 634N

Multiple Choice

•Which graph best represents the greatest amount of work?

• 1

• 2

• 3

• 4