Kinetic and gravitational potential energy
KE = ½mv²; GPE = mgh.
The common mistake
Forgetting to square the speed, or dropping the ½ in kinetic energy.
Instead: Square v before multiplying, then halve. Doubling speed makes KE four times bigger.
Worked example with Guide me
Find the kinetic energy of a 2 kg ball at 3 m/s.
- Sugar · Square the speed.Student · 9.
- Sugar · ½ × 2 × 9?Student · 9.
Answer: 9 J
Try 3 practice questions
1. GPE of 5 kg lifted 2 m (g = 10)?
Show answer
100 J
2. KE of 4 kg at 5 m/s?
Show answer
50 J
3. If speed doubles, KE becomes…?
Show answer
4 times bigger
Quick answers
- What is the most common mistake with kinetic and gravitational potential energy?
- Forgetting to square the speed, or dropping the ½ in kinetic energy.
- How do I get kinetic and gravitational potential energy right?
- Square v before multiplying, then halve. Doubling speed makes KE four times bigger.
- Can you show a worked example?
- Find the kinetic energy of a 2 kg ball at 3 m/s. 9 J
Related concepts
Save this as a miss — practice it before your test
Sugar brings it back for review until it sticks. Free, no card.
Save this as a miss — practice it before your test