Energy changes form

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. 1.

   A cart starts at rest with 1200 J stored at 30 m. Stored energy is proportional to height. At 10 m, 200 J is thermal. What is its motion energy, Bo?

   600 J
2. 2.

   Esme's sled has 900 J stored at the top, 15 m up. Stored energy is proportional to height. At 5 m, 50 J is thermal. What is the motion energy?

   550 J
3. 3.

   Kira wants the cart to clear a taller second hill. Which change would help most?

   • More friction on the track
   • Painting the cart a faster color
   • A longer flat part before the hill
   • A taller first hill
4. 4.

   A test cart stops just short of the top of a hill that is lower than the start. What explains it, Luz?

   • Friction made some thermal energy
   • The cart gained too much energy
   • Energy runs out on long tracks like this one
   • The track destroyed some energy
5. 5.

   Milo says a coaster ride uses up energy, so there is less energy in the world afterward. Agree or disagree?

   • Agree: the brakes destroy it
   • Agree: rides use up energy
   • Disagree: it changed form
   • Disagree: there is more afterward
6. 6.

   Noah's bars show 700 J stored at the top and 640 J motion at the bottom, so Noah says 60 J vanished. Agree or disagree?

   • Disagree: 60 J was added
   • Agree: the bars no longer add to 700 J
   • Disagree: 60 J became thermal energy and sound
   • Agree: 60 J was destroyed
7. 7.

   Pia says a sled gains energy sliding downhill, because it speeds up. Agree or disagree?

   • Disagree: it loses its energy
   • Agree: the slope gives it free energy
   • Agree: speeding up adds new energy
   • Disagree: stored energy becomes motion energy
8. 8.

   A cart starts with 400 J stored. Ren checks three classmates' bars for the bottom of the hill. Which set can be right?

   • Motion 350 J and thermal 0 J
   • Motion 350 J and thermal 50 J
   • Motion 450 J and thermal 50 J
   • Motion 0 J and thermal 0 J
9. 9.

   A bike starts with 1,000 J stored at the top. Which set of bars at the bottom can be right, Tala?

   • Motion 1,100 J and thermal 0 J
   • Motion 880 J and thermal 0 J
   • Motion 500 J and thermal 0 J
   • Motion 880 J and thermal 120 J
10. 10.

    A sled starts with 650 J stored. Halfway down, which set of bars can be right, Zee?

    • Stored 300 J, motion 400 J, thermal 30 J
    • Stored 300 J, motion 320 J, thermal 0 J
    • Stored 300 J, motion 0 J, thermal 0 J
    • Stored 300 J, motion 320 J, thermal 30 J