IB MYP 4-5 Physics- Kinetic energy- Study Notes - New Syllabus
IB MYP 4-5 Physics-Kinetic energy- Study Notes
Key Concepts
- Kinetic energy
Kinetic Energy
Kinetic Energy
Kinetic energy is the energy possessed by a body due to its motion. Any object that is moving has kinetic energy, regardless of its direction of travel.
Formula for Kinetic Energy:
\( KE = \dfrac{1}{2}mv^2 \)
- \( KE \) = Kinetic Energy (in joules, J)
- \( m \) = mass of the object (in kilograms, kg)
- \( v \) = velocity of the object (in meters per second, m/s)
Key Notes:
- Kinetic energy is directly proportional to the mass of the object.
- Kinetic energy is directly proportional to the square of the velocity. This means doubling the velocity will increase kinetic energy by a factor of 4.
- The unit of kinetic energy is the joule (J), where \( 1\, \text{J} = 1\, \text{kg·m}^2/\text{s}^2 \).
- If velocity is zero, the kinetic energy is zero.
Conversion of Kinetic Energy:
- Kinetic energy can be converted into other forms such as heat, sound, or potential energy (e.g., in pendulums or roller coasters).
- In the absence of friction and air resistance, kinetic energy and potential energy can interchange without loss of total mechanical energy.
Example:
A car of mass \( 1200\, \text{kg} \) is moving at a speed of \( 20\, \text{m/s} \). Calculate its kinetic energy.
▶️ Answer/Explanation
\( KE = \dfrac{1}{2}mv^2 \)
\( KE = \dfrac{1}{2} \times 1200 \times (20)^2 \)
\( KE = 600 \times 400 \)
\( KE = \mathbf{240,000 \, J} \)
Example:
A cyclist with a total mass of \( 80\, \text{kg} \) (including the bicycle) has \( 640\, \text{J} \) of kinetic energy. Find the cyclist’s speed.
▶️ Answer/Explanation
\( KE = \dfrac{1}{2}mv^2 \)
\( 640 = \dfrac{1}{2} \times 80 \times v^2 \)
\( 640 = 40 \times v^2 \)
\( v^2 = 16 \)
\( v = \mathbf{4\, m/s} \)