CIE iGCSE Co-ordinated Sciences-P1.6.2 Work- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P1.6.2 Work – Study Notes
CIE iGCSE Co-ordinated Sciences-P1.6.2 Work – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Understand that mechanical or electrical work done is equal to the energy transferred.
- Recall and use the equation for mechanical working: $W = Fd = \Delta E$.
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Work Done and Energy Transfer
Work done is a measure of energy transfer when a force moves an object, or when electrical energy is transferred by a current. In all cases, mechanical or electrical work done = energy transferred.
Mechanical Work Done:
When a force \( F \) moves an object a distance \( d \) in the direction of the force, work is done.
Equation: \( W = F \times d \)
- \( W \) = work done (J, joules)
- \( F \) = force applied (N, newtons)
- \( d \) = distance moved in the direction of the force (m)
Key Note: Work done transfers energy from one store to another. For example, lifting a book transfers chemical energy from muscles → gravitational potential energy of the book.
Work Done: Positive, Negative, and Zero
Work done by a force can be positive, negative, or zero, depending on the direction of the force relative to the displacement.
1. Positive Work
- Occurs when the force has a component in the same direction as the displacement of the object.
- Energy is transferred to the object, increasing its energy.
Example:
Pushing a box along the floor → the box speeds up; energy is transferred to kinetic energy.
2. Negative Work
- Occurs when the force has a component in the opposite direction to the displacement.
- Energy is transferred from the object, decreasing its energy.
Example:
Friction acting on a sliding book slows it down → kinetic energy decreases; work done by friction is negative.
3. Zero Work
- Occurs when the force is perpendicular to the displacement or when there is no displacement.
- No energy is transferred in the direction of the force.
Example:
Carrying a bag at constant height while walking horizontally → force upward (weight) is perpendicular to horizontal displacement → work done by weight is zero.
Electrical Work Done:
When a current flows through a component with potential difference \( V \) for a time \( t \), electrical energy is transferred.
Equation: \( W = V I t \)
- \( W \) = work done / energy transferred (J, joules)
- \( V \) = potential difference (V, volts)
- \( I \) = current (A, amperes)
- \( t \) = time (s, seconds)
Example:
A person pushes a box across the floor 5 m, but friction acts backward. Calculate positive and negative work.
▶️ Answer/Explanation
Force applied by person: \( F_\text{push} = 60~\text{N} \)
Friction force: \( F_\text{friction} = 10~\text{N} \) (opposite direction)
Positive work: \( W_\text{push} = F \times d = 60 \times 5 = 300~\text{J} \)
Negative work: \( W_\text{friction} = – F \times d = -10 \times 5 = -50~\text{J} \)
Net work done on the box: \( 300 – 50 = 250~\text{J} \)
Example:
A person pushes a box with a force of \( 50~\text{N} \) for a distance of \( 4~\text{m} \) along the floor. Calculate the work done.
▶️ Answer/Explanation
Equation: \( W = F \times d \)
\( W = 50 \times 4 = 200~\text{J} \)
The person transfers 200 J of energy to the box.
Example:
A 12 V battery powers a lamp with a current of 2 A for 3 minutes. Calculate the energy transferred.
▶️ Answer/Explanation
Convert time: \( 3~\text{minutes} = 180~\text{s} \)
Equation: \( W = V I t \)
\( W = 12 \times 2 \times 180 = 4320~\text{J} \)
The lamp receives 4320 J of energy from the battery.
Mechanical Work Done
Mechanical work is done when a force moves an object through a distance in the direction of the force. Work done is equal to the energy transferred.
Equation:
\( W = F \times d = \Delta E \)
- \( W \) = work done (J, joules)
- \( F \) = force applied (N, newtons)
- \( d \) = displacement in the direction of the force (m)
- \( \Delta E \) = energy transferred (J, joules)
Key Notes:
- Work done by a force transfers energy to or from an object.
- If the force is in the direction of motion → positive work → energy increases.
- If the force is opposite to the motion → negative work → energy decreases.
- If the force is perpendicular to displacement → zero work → no energy transfer in that direction.
Example:
A person lifts a 5 kg box vertically by 2 m. Calculate the work done.
▶️ Answer/Explanation
Force required to lift: \( F = m g = 5 \times 9.8 = 49~\text{N} \)
Displacement: \( d = 2~\text{m} \)
Work done: \( W = F \times d = 49 \times 2 = 98~\text{J} \)
Energy transferred: 98 J → gravitational potential energy of the box.
Example :
A 20 N frictional force slows a sliding box over 3 m. Calculate the work done by friction.
▶️ Answer/Explanation
Friction acts opposite to displacement → work is negative.
\( W = – F \times d = – 20 \times 3 = -60~\text{J} \)
The kinetic energy of the box decreases by 60 J.