Motion (kinetic) energy, and how mass and speed change it

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. 1.

   Ari's cart has 20 J of motion energy at 2 m/s. Its speed rises to 6 m/s. What is its motion energy now?

   180 J
2. 2.

   Bo's scooter has 10 J of motion energy at 1 m/s. Then it speeds up to 4 m/s. What is its motion energy now?

   160 J
3. 3.

   A ball has 30 J of motion energy at 2 m/s. Esme rolls it again at 4 m/s. What is its motion energy now?

   120 J
4. 4.

   In the lab, Kira watches a heavy cart bump a light one. What do the bars show?

   • The light cart got less since it is lighter
   • The light cart made 14 J of new energy
   • Energy moved to the light cart, and 2 J to heat and sound
   • 2 J was destroyed in the bump
5. 5.

   Luz rubs both hands together fast, and they feel warm. What happened to the motion energy?

   • It stayed as motion energy
   • It was used up by the rubbing
   • Bigger hands lose it faster
   • It turned into thermal energy
6. 6.

   Milo says riding twice as fast doubles a bike's motion energy. Agree or disagree?

   • Agree: energy and speed match
   • Disagree: it becomes four times as much
   • Agree: double the speed gives double the energy
   • Disagree: speed doesn't change it
7. 7.

   Noah says a 2 kg cart at 3 m/s and a 3 kg cart at 2 m/s have equal motion energy. Agree or disagree?

   • Agree: 2 × 3 equals 3 × 2
   • Agree: speed and mass count the same
   • Disagree: the faster cart has more
   • Disagree: the heavier cart has more
8. 8.

   Pia says a twice-as-heavy wagon at the same speed has four times the motion energy. Agree or disagree?

   • Disagree: mass doesn't matter
   • Disagree: it has twice as much
   • Agree: heavier means four times
   • Agree: mass is squared too
9. 9.

   To cut a cart's motion energy the most, should Ren halve its speed or halve its mass?

   • Neither changes the energy
   • Halve the mass: mass counts more
   • Halve the speed: energy drops to a quarter
   • Either: both give half
10. 10.

    Zee unloads a cart from 60 kg to 40 kg, at the same speed. How does its motion energy change?

    • It doubles
    • It does not change at the same speed
    • It drops by more, since mass is squared
    • It drops by a third