Give three factors that affected the kinetic energy of the person as she reached the bottom of the zip wire.
How to approach this question
1. Start with the equation for kinetic energy: KE = ½mv². What two factors are in this equation?
2. Think about where the kinetic energy comes from. It's a conversion from gravitational potential energy (GPE). What factors affect the initial GPE?
3. Consider why not all the GPE is converted to KE. What forces act against the motion of the person?
Full Answer
The kinetic energy (KE) of the person at the bottom depends on the energy transfers that have occurred.
1. **Energy Source:** The primary source of energy is the gravitational potential energy (GPE) the person has at the top. The amount of GPE depends on the person's **mass** and the **vertical height** they descend.
2. **Energy Conversion:** As the person slides down, GPE is converted into KE. In a perfect system, GPE lost = KE gained.
3. **Energy Losses:** In reality, some energy is transferred to the surroundings due to work done against resistive forces. These include **air resistance** (drag) acting on the person and **friction** between the harness and the zip wire.
Therefore, the final kinetic energy is affected by the initial GPE (determined by mass and height) and the energy lost to friction and air resistance.
Common mistakes
✗ Just stating "gravity". Gravity is the force that causes the acceleration, but the factors affecting the energy are mass and height.
✗ Listing factors that don't affect the energy, like "the weather" (unless linked to wind/air resistance) or "the length of the wire" (it's the vertical drop that matters for GPE).
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