Stored (potential) energy

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. 1.

   Ari lifts a 2 kg bag up a staircase, and it gains 120 J of stored energy. With g = 10 N/kg, how high was it lifted?

   6 m
2. 2.

   A 5 kg box is lifted onto a loading dock and gains 150 J of stored energy, Bo reads. With g = 10 N/kg, how high was it lifted?

   3 m
3. 3.

   Jun moves a box to half the height, then adds a second identical box on top. How does the stored energy compare?

   • It is zero: the boxes are still
   • It halves: height is what counts
   • It is the same as before
   • It doubles: the load is heavier
4. 4.

   A 3 kg pot sits on a 2 m shelf and a 2 kg pot on a 3 m shelf. Which stores more energy, Kira?

   • The 3 kg pot
   • They store the same
   • The pot on the 3 m shelf
   • Neither, since both are still

5. Read this first

   Three objects on shelves (example data)

   object	mass (kg)	height (m)
   P	1	6
   Q	3	1
   R	2	4

6. 5.

   Luz's table lists three objects on shelves. Which stores the most energy from gravity?

   • R
   • They are the same
   • P, the highest one
   • Q, the heaviest one
7. 6.

   Noah throws a ball straight up. A friend says it stores the most energy just as it leaves the hand, where it is fastest. Agree or disagree?

   • Disagree: it stores the most at the top
   • Agree: fastest means the most stored
   • Agree: the hand gives it stored energy
   • Disagree: nothing is stored while moving
8. 7.

   Pia holds a stretched band still and says it has energy only once it is let go. Agree or disagree?

   • Agree: it gets energy from moving
   • Disagree: it stores sound energy
   • Disagree: it already stores elastic energy
   • Agree: still things have no energy
9. 8.

   Ren rolls a skateboard on a U-shaped ramp. It reaches a little lower on the other side. Where did the missing 10 J go?

   • To thermal energy and sound
   • It was used up and is gone
   • It stayed as motion energy at the top
   • Into more stored energy

10. Use this

    Energy bar chart (example data), one bar per energy store, height in J. Ball held at 1 m: stored 5 J; thermal and sound 0 J. Top of the first bounce: stored 3 J; thermal and sound ?. A transfer arrow goes from motion to thermal and sound, labeled bounce.

11. 9.

    Tala drops a ball; it bounces back lower. How much energy went to thermal energy and sound?

    • 2 J
    • 8 J
    • 0 J; 2 J was destroyed
    • 3 J
12. 10.

    Zee lets a swing go and waits until it stops. What happened to the 300 J?

    • It ran out and is gone
    • It turned back into the push
    • It became 300 J of thermal energy
    • It is still stored in the swing