IB MYP 4-5 Physics- Work- Study Notes - New Syllabus
Work
Work
Work is done when a force is applied to an object and the object is displaced in the direction of the force. It represents the transfer of energy from one form to another due to motion under a force.
Work is the product of the component of the force in the direction of displacement and the magnitude of the displacement.
W = F \cdot d \cdot \cos\theta
- W = Work done (Joules, J)
- F = Magnitude of the applied force (Newtons, N)
- d = Displacement of the object (meters, m)
- \(\theta\) = Angle between the force and displacement directions
Conditions for Work to be Done:
- A force must be applied.
- The object must be displaced.
- There must be a component of force in the direction of displacement.
Positive and Negative Work:
- Positive work: Force component is in the same direction as displacement (energy is given to the object).
- Negative work: Force component is opposite to the displacement (energy is taken from the object).
Special Cases:
- If \(\theta = 0^\circ\), \(W = F \cdot d\) → maximum work.
- If \(\theta = 90^\circ\), \(W = 0\) → no work is done (e.g., centripetal force in uniform circular motion).
Unit of Work:
- SI unit: Joule (J)
- 1 Joule = Work done when a force of 1 N displaces an object by 1 m in the direction of the force.
Example:
A person pushes a box with a force of \(50 \ \mathrm{N}\) over a distance of \(4 \ \mathrm{m}\) at an angle of \(30^\circ\) to the horizontal. Find the work done.
▶️ Answer/Explanation
W = \(F \cdot d \cdot \cos\theta\)
= \(50 \cdot 4 \cdot \cos 30^\circ\)
= \(200 \cdot 0.866\)
= \(173.2 \ \mathrm{J}\)
\(\boxed{173.2 \ \mathrm{J}}\)
Example:
Why does carrying a heavy load while walking on a flat surface not require work in physics terms?
▶️ Answer/Explanation
Work depends on the component of force in the direction of displacement.
When walking horizontally, the vertical force due to holding the load is perpendicular to the horizontal displacement.
Since \(\theta = 90^\circ\), \(\cos 90^\circ = 0\), so \(W = 0\).
Thus, in physics terms, no work is done, even though you feel tired due to biological energy expenditure.