Explanation:
We need to decide whether each object has
kinetic energy (energy of motion) or
potential energy (stored energy due to position/height).
Key ideas:
- If an object is
moving, it has
kinetic energy.
- If an object is
at a height (and not moving *at that moment*), it has
gravitational potential energy.
- For potential energy, we often use weight (in newtons, N) and height (in meters, m):
Potential Energy = weight × height
(Because weight = mg, so PE = mgh = weight × height — this avoids needing mass separately.)
Let’s go through each problem:
1. Volleyball served at 30 m/s → It’s moving →
kinetic energy
(Even though it’s also at some height, the question only gives speed, not height, and says “leaves your hand” — focus on motion.)
2. Baby carriage sitting at top of 21 m hill → Not moving (sitting), at height →
potential energy
3. Car traveling at 40 m/s → Moving →
kinetic energy
4. Cinder block sitting on platform 20 m high → Not moving, at height →
potential energy
5. Bell at top of 45 m tower → Not moving (just sitting there), at height →
potential energy
6. Roller coaster at top of 72 m hill → At that moment, it’s at the top — typically momentarily at rest before dropping → So
potential energy
(The problem says “at this moment”, and gives no speed — assume it’s paused or just reached the top.)
Now, double-check:
- Problems 1 and 3 involve speed → kinetic.
- Problems 2, 4, 5, 6 involve height and no mention of motion → potential.
All consistent.
Final Answer:
1. kinetic
2. potential
3. kinetic
4. potential
5. potential
6. potential
Parent Tip: Review the logic above to help your child master the concept of kinetic energy problems worksheet.
