GED Science TestPhysical ScienceHard
A student drops a 0.2 kg ball from a height of 10 meters. Ignoring air resistance, what is the kinetic energy of the ball just before it hits the ground? (Use g = 9.8 m/s²)
- A196 J
- B19.6 J
- C200 J
- D1.96 J
Show answer & explanationAnswer & explanation
Correct answer: B. 19.6 J
According to the Law of Conservation of Mechanical Energy, the potential energy at the top is converted into kinetic energy at the bottom. Potential Energy (PE) = mgh. So, PE = 0.2 kg × 9.8 m/s² × 10 m = 19.6 J. Therefore, the kinetic energy just before impact is 19.6 J.
Why the other options are wrong
- A. This is a calculation error (possibly 0.2 * 9.8 * 100 or 2 * 9.8 * 10).
- C. This might come from using g=10 and rounding, but is not the most accurate answer given g=9.8.
- D. This is a calculation error (possibly 0.2 * 9.8 * 1).
Conservation of Mechanical Energy
The Law of Conservation of Mechanical Energy states that in an isolated system, the total mechanical energy (sum of kinetic and potential energy) remains constant if only conservative forces (like gravity) are doing work.
- Total Mechanical Energy = Kinetic Energy + Potential Energy
- PE_initial + KE_initial = PE_final + KE_final
- Potential Energy (gravitational) = mgh
- Kinetic Energy = 0.5mv²
Memory trick: PE converts to KE, Energy is Conserved