Stored (potential) energy

Answer Key - Grade 8 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari lifts a 2 kg backpack onto a shelf 3 m above the floor. Use PE = m × g × h with g = 10 N/kg. How much stored energy does it gain?

   60 J
2. 2.

   Bo lifts a 4 kg box of books onto a closet shelf 2 m up. Use PE = m × g × h with g = 10 N/kg. How much stored energy does it gain?

   80 J
3. 3.

   A teacher helps Esme raise a 3 kg bucket 5 m with a pulley. Use PE = m × g × h with g = 10 N/kg. How much stored energy does it gain?

   150 J
4. 4.

   Jun puts the same ball on a low shelf (A, 0.5 m) and a high shelf (B, 2 m). Which stores more energy?

   • A, since it is easier to reach
   • B, the higher shelf
   • Neither: a still ball has no energy
5. 5.

   Kira holds a skateboard still at the top (P) and middle (Q) of a ramp. Where does it store more energy?

   • At P, the higher point
   • Neither, since it is held still
   • At Q, where it would move faster
6. 6.

   Luz has two copies of the same book: one on the floor and one on a desk. Which stores more energy from gravity?

   • Both store no energy, since both are still
   • The floor book, since it could slide fastest
   • The one on the desk
7. 7.

   Milo stretches a rubber band and holds it still. What kind of energy does it store?

   • Motion energy, since it could fly off
   • Elastic stored energy
   • Sound energy
   • No energy, since it is still
8. 8.

   Pia holds two magnets a little apart; they pull toward each other. What kind of energy do they store?

   • No energy until they snap together
   • Magnetic stored energy
   • Motion energy
   • Thermal energy

9. Read this first

   Use this

   Energy bar chart (example data), one bar per energy store, height in J. Band stretched: elastic stored 12 J; motion 0 J. Toy just leaves the band: elastic stored 0 J; motion ?. A transfer arrow goes from elastic stored to motion, labeled launch. Friction and sound are small enough to leave out.

10. 9.

    Tala launches a foam toy with a stretched band. How much motion energy does the toy have as it leaves?

    • 12 J
    • 0 J, the band used it
    • 6 J, half used up
11. 10.

    Zee swings at the park. How much motion energy does Zee have at the lowest point?

    • 200 J
    • 100 J
    • 0 J