Potential Energy – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Explain how a stretched rubber band stores energy. Why does it snap back on release?
Answer:
- When you pull a rubber band, you do work on it.
- This work gets stored as elastic potential energy in the stretched band.
- The rubber band wants to return to its original shape.
- A restoring force pulls it back when you release it.
- The stored energy changes into kinetic energy, sound, and a little heat.
- More stretch means more stored potential energy, up to its elastic limit.
Q2. Describe the gravitational potential energy of a lifted object. What factors affect it?
Answer:
- When you lift an object, you work against gravity.
- This work is stored as gravitational potential energy (GPE).
- GPE depends on mass (m), height (h), and gravity (g).
- In simple form: GPE = m × g × h (mgh).
- If you double the height, GPE doubles.
- If you double the mass, GPE also doubles.
Q3. How does a winding key make a toy car move? Explain the role of windings.
Answer:
- Turning the key twists a spring inside the car.
- Your work stores elastic potential energy in the spring.
- When released, this turns into kinetic energy of the wheels.
- More windings usually store more energy, so the car moves farther.
- But too many windings can reach a limit and may damage the spring.
- The car stops due to friction and air resistance.
Q4. A slinky is stretched and also compressed. Does it store energy in both cases? Explain.
Answer:
- Yes, both stretching and compressing store energy.
- The energy stored is elastic potential energy.
- The slinky obeys Hooke’s Law for small stretches and compressions.
- Greater deformation (within limits) means more energy stored.
- When released, energy changes into motion of the coils.
- If stretched too much, it crosses the elastic limit and may deform.
Q5. Describe the energy changes when you shoot an arrow using a bow.
Answer:
- Your muscles do work to pull the string.
- This work is stored as elastic potential energy in the bent bow.
- On release, it converts into the arrow’s kinetic energy.
- More draw length means more energy stored, so the arrow goes faster.
- Some energy is lost as sound, heat, and vibration of the bow.
- Good technique reduces energy loss and improves range.
High Complexity (Analysis & Scenario-Based)
Q6. Two identical balls are lifted to heights h and 2h. Compare their potential energies and final speeds when dropped.
Answer:
- GPE at height h is mgh; at 2h it is 2mgh.
- So, the ball at 2h has double the potential energy.
- On falling, GPE changes into kinetic energy.
- Ignoring air, final speed from height h is √(2gh).
- From 2h, final speed is √(4gh) = √2 × √(2gh).
- So the higher drop gives more energy and higher speed.
Q7. Two rubber bands (A thin, B thick) are stretched by the same length x. Which stores more energy? Justify.
Answer:
- Energy in a stretched band is (1/2) k x², where k is stiffness.
- A thicker band usually has a larger k (more stiff).
- With the same extension (x), a larger k gives more energy stored.
- So the thick band stores more elastic potential energy.
- If you apply the same force instead, the thicker band stretches less.
- Still, due to higher k, it can store more energy for the same x.
Q8. A wound toy car travels farther on a smooth floor than on a carpet. Explain why.
Answer:
- The spring gives the car kinetic energy to move.
- On carpet, friction and rolling resistance are higher.
- More energy is lost as heat in the carpet fibers.
- On a smooth floor, energy loss is lower, so it travels farther.
- Air resistance is similar, but surface friction is the main factor.
- Thus, distance depends on energy losses to the surroundings.
Q9. A student says, “Potential energy is only due to height.” Evaluate this statement with examples.
Answer:
- The statement is not fully correct.
- Height gives gravitational potential energy like mgh.
- But stretched bands, slinkies, and springs store elastic potential energy.
- A wound toy car stores energy in a twisted spring.
- A bent bow stores energy in its deformation.
- So, potential energy depends on position or configuration, not only height.
Q10. Design an experiment to show that GPE depends on both mass and height. State steps and precautions.
Answer:
- Take two masses (m and 2m), a table, a soft landing area, and a meter scale.
- Lift mass m to heights h and 2h, and note the drop impact or sound.
- Repeat with mass 2m at height h.
- Compare effects: higher h or higher m gives more impact, showing more GPE.
- Record observations and conclude: GPE ∝ m and GPE ∝ h.
- Precautions: keep the area safe, drop from the same spot, and avoid air drafts.