Force, mass and acceleration

Answer Key - Grade 8 Science Worksheet - Challenge Me

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

1. 1.

   Ari pushes a loaded wagon with 96 N against 16 N of friction. It speeds up at 4 m/s². What is its mass?

   20 kg
2. 2.

   Bo pushes a box with 90 N against 30 N of friction. It speeds up at 5 m/s². What is its mass?

   12 kg
3. 3.

   Esme pushes a shopping cart with 56 N against 20 N of friction. It speeds up at 2 m/s². What is its mass?

   18 kg
4. 4.

   Kira's sled gets half the push but carries twice the mass. What happens to its acceleration?

   • It doubles: more mass speeds it
   • It halves: the push matters most
   • It is one quarter as much
   • It moves at a slower steady speed

5. Read this first

   Use this

   Force arrow diagram, one dimension, arrows drawn to scale by size. Box A labeled 10 kg: push 30 N pointing right; friction 10 N pointing left. Box B labeled 20 kg: push 30 N pointing right; friction 0 N pointing left.

6. 5.

   Milo compares two carts. Which has the greater acceleration?

   • Cart B, since it has more mass
   • Cart A
   • The same, since both get 30 N pushes
   • Cart B, since it has no friction
7. 6.

   Noah compares two sleds. Which has the greater acceleration?

   • Sled A, since it is heavier
   • Sled A, since its pull is bigger
   • Sled B
   • They are equal
8. 7.

   Pia compares two boxes pushed with 25 N each. How do their accelerations compare?

   • They are equal
   • Box B's is bigger, since it is heavier
   • Box B's is bigger, since its friction is less
   • Box A's is bigger: 25 ÷ 5 beats 25 ÷ 10

9. Use this

   Investigation card (test results). Question: does more force give more acceleration? Trial 1: 2 kg cart, 4 N pull, 2 m/s². Trial 2: 4 kg cart, 8 N pull, 2 m/s². Conclusion written: force does not change acceleration.

10. 8.

    Ren checks a classmate's test. What is wrong with the conclusion?

    • The track should have been longer
    • The pulls were too small to matter
    • Speed, not acceleration, should be measured
    • Two things changed at once: force and mass

11. Use this

    Investigation card (test results). Question: how does pulling force change a 3 kg cart's motion? Changed: pull (3 N, 6 N). Measured: the cart's speed after 1 s, starting from rest. Results: 1 m/s, 2 m/s. Conclusion written: each force gives the cart one fixed speed.

12. 9.

    Tala reads this conclusion. What is the best correction?

    • The mass changed between trials
    • The cart should be lighter
    • The force changed how fast speed grows
    • Each force gives a fixed speed, as written

13. Use this

    Investigation card (test results). Question: does mass change acceleration with the same pull? One trial each: 1 kg cart, 2 m/s²; 2 kg cart, 1 m/s². The pulls were not measured. Conclusion written: more mass gives less acceleration.

14. 10.

    Zee checks this test. What makes the conclusion weak?

    • More mass should give more acceleration
    • The carts were too light
    • The pulls were not measured or repeated
    • Speed should be measured instead