Grade 10 Physics: Work & Energy

Work & Energy

• This presentation is for Grade 10 Physics students at Saint Jude Catholic School.
• The teachers are Mr. Jerome Morales and Mr. Carl Fermil Aguinaldo.

Activity

• Students are asked to bring random objects from home.
• The first student to show their object is awarded a recitation chip.

Bring Me Items

• Item #1: One Peso Coin
• Item #2: Pair of Socks
• Item #3: Physics Notebook
• Item #4: Chemistry Textbook (Glencoe)
• Item #5: Biology Textbook (Glencoe Biology) with Chemistry Textbook (Glencoe)

Processing Questions

• What have you noticed with the order of the items asked to bring to the camera?
• What are the steps you did to bring the books in front of the camera? (Be as detailed as possible.)
• Can you say that the force you exerted caused the items to be displaced from where they were to where they are now?

Learning Objectives

• Identify situations where work is done and where no work is done.
• Differentiate potential and kinetic energy and their practical applications.
• Identify and explain factors affecting potential and kinetic energy.
• Solve problems involving work and energy.
• State and explain the work-energy theorem and give examples for each.

The Work Concept

Work

• Work is a quantity resulting from a force causing movement over a distance.
• Mathematically, Work (W) = Force (F) × Displacement (d)

The Joule Unit

• One Joule (J) of work equals one Newton (N) of force applied to move an object one meter (m).
• 1 Joule = 1 Newton × 1 meter

The Parallel Condition

• Work is only done when the force applied is parallel to the direction of movement.
• If the object moves at an angle, only the component of displacement parallel to the force produces work.
• Work = Force × Displacement × cosine of the angle ( θ )

Work or No Work?

• Work is done when a force causes movement in the direction of the force.

Pushing a Table

• Pushing a table involves doing work.

Sitting Down

• Sitting down does not involve doing work.

Carrying Grocery Bags While Walking

• Carrying grocery bags while walking does not involve doing work (as long as there isn't a change in the height of the load).

Practice Problems (Examples)

• Suppose you push a chair with a 500 N force along a 7 m aisle. How much work is done?
• Suppose you apply a 60 N horizontal force to a 32 kg package, which pushes it 4 meters across a floor. How much work do you do on the package?
• Five football players push a 300 kg sled across the field. The sled is accelerating at 0.25 m/s² with negligible friction. What is the work done on the sled by the football player over 15.0 m of pushing?
• Determine the work done when you exert a force of 3 N at an angle of 45 degrees from the direction of motion for 1 m.
• A 5 kg object traveled 12 meters on an inclined plane at an angle of 30 degrees from the floor. If the object's acceleration is 4 m/s², what amount of work is done on the object?

Positive, Negative, and Zero Work

• Positive Work: The force and displacement are in the same direction (angle between them is less than 90°).
• Negative Work: The force and displacement are in opposite direction (angle between them is more than 90°).
• Zero Work: The force is perpendicular to the displacement (angle between them is 90°).

What Does a Negative Work Mean?

• Negative work indicates that the force is opposing the motion, potentially slowing it down, and reducing the kinetic energy of the object.

Example of Positive and Negative Work

• An apple falling from a tree experiences positive work from gravity.
• Air resistance acting on a falling apple causes negative work because the force of air resistance is opposite to the direction of the apple's displacement.