Balanced forces, equilibrium and inertia

Answer Key - Grade 11 Science Worksheet - Challenge Me

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

1. 1.

   Ari hauls a 20 kg crate up a 30° ramp at constant velocity with a rope parallel to the ramp. Sliding friction is 25 N. What is the rope's tension, to 0.1 N?

   123 N
2. 2.

   Bo hauls a 12 kg crate up a 25° ramp at constant velocity with a rope parallel to the ramp. Sliding friction is 18 N. What is the rope's tension, to 0.1 N?

   67.7 N
3. 3.

   Esme hauls a 50 kg crate up a 37° ramp at constant velocity with a rope parallel to the ramp. Sliding friction is 60 N. What is the rope's tension, to 0.1 N?

   354.9 N
4. 4.

   “example data” Using the diagram, which cable has the greater tension, Luz?

   • Neither cable: both pull 98 N, by the symmetry of the sign
   • The left cable, since 30° is the smaller angle
   • The right cable, at 60°, since it carries more of the weight
   • The left cable, at 30°, since a flatter cable pulls much harder
5. 5.

   Milo says a skydiver falling at a steady speed has no forces acting. Agree or disagree?

   • Disagree: gravity acts alone, so the diver speeds up
   • Agree: drag appears when the diver speeds up
   • Disagree: drag and weight both act, and they cancel
   • Agree: a steady speed means that no force acts on the diver
6. 6.

   Noah says a block sliding down a ramp at a steady speed must have no friction. Agree or disagree?

   • Agree: sliding means gravity's part beats friction on the block
   • Agree: a steady speed means no friction acts on the sliding block
   • Disagree: friction up the ramp balances the weight's part down it
   • Disagree: friction is larger than gravity's part, so the block slows
7. 7.

   A 2,000 kg truck and 1,000 kg car go equally fast. Pia says the same braking force stops both in the same distance. Agree or disagree?

   • Agree: braking force depends on speed, not on mass
   • Agree: they start at the same speed, so both stop in the same distance
   • Disagree: the car needs twice the distance, since it is lighter
   • Disagree: the truck has twice the inertia and needs twice the distance
9. 8.

   A ball hangs from a train ceiling as the train speeds up, and the string tilts. Seen from the ground, what supplies the ball's forward acceleration, Ren?

   • The horizontal part of its weight, pointing toward the front
   • A forward force carried over from the train's motion
   • Its own inertia pushing it forward as the train speeds up
   • The horizontal part of the string's tension
10. 9.

    The string stays 30° from the vertical while the train speeds up. What is the train's acceleration, Tala?

    Use the picture in question 8.

    • About 8.5 m/s²
    • About 4.9 m/s²
    • About 5.7 m/s²
    • About 17 m/s²
11. 10.

    In a jet cruising at a steady 250 m/s, Zee drops a coin. Where does it land compared with the feet?

    • Ahead of the feet, since the jet's speed adds to the coin's fall
    • Several meters behind the feet, since the jet moves on
    • At the feet, since it keeps the jet's forward velocity
    • Behind the feet, since the air in the cabin holds it back