Draw free-body diagrams and find the net force

Answer Key - Grade 11 Science Worksheet - Challenge Me

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

1. 1.

   Bo pulls a 20 kg wagon with 100 N at 30° above the ground. The sliding friction coefficient is 0.3. To 0.01 m/s², what is its acceleration?

   2.14 m/s²
2. 2.

   Esme pulls a 8 kg wagon with 40 N at 60° above the ground. The sliding friction coefficient is 0.25. To 0.01 m/s², what is its acceleration?

   1.13 m/s²
3. 3.

   Two free-body diagrams side by side (example data). Using the diagrams, about what is the rope's tension, Kira?

   • About 7.8 N, which is 2 kg × 3.92 m/s²
   • About 29.4 N, the weight of the block on the table
   • About 19.6 N, the weight of the hanging block
   • About 11.8 N, which is 3 kg × 3.92 m/s²

4. Read this first

   Free-body diagram (example data)

   a block sliding down a 30° ramp of mass 4 kg, with arrows from its center: weight 39.2 N straight down; normal force 33.9 N out of the ramp; sliding friction 6.8 N up the ramp.

5. 4.

   Using the diagram, about what is the block's acceleration down the ramp, Luz?

   • About 4.9 m/s² down the ramp, ignoring friction
   • About 3.2 m/s² down the ramp
   • About 1.7 m/s² down the ramp, from 6.8 ÷ 4
   • About 6.6 m/s² down the ramp, adding friction
6. 5.

   Milo says the normal force on a block on a 30° ramp equals its weight. Agree or disagree?

   • Agree: the surface always pushes back with the full weight
   • Agree: the ramp's tilt changes the weight but not the normal force
   • Disagree: the normal force is larger than the weight on a ramp
   • Disagree: it balances only the weight's part into the ramp
7. 6.

   Noah says a scale in a rising elevator always reads more than the person's weight. Agree or disagree?

   • Disagree: the scale reads less when the elevator is moving up
   • Disagree: it reads more only if the lift speeds up upward
   • Agree: moving upward adds to the person's weight on the scale
   • Agree: the scale reads the elevator's speed times the mass
8. 7.

   Pia says that with no air, a heavier ball falls faster because gravity pulls it harder. Agree or disagree?

   • Agree: a bigger weight means a bigger acceleration
   • Agree: heavier balls reach the ground first, as experiments show
   • Disagree: the extra pull is cancelled by the extra mass, so a = g
   • Disagree: lighter balls fall faster because they have less weight

9. Free-body diagram (example data)

   a box on a truck bed that is speeding up forward of mass 10 kg, with arrows from its center: weight 98 N down; normal force 98 N up; friction from the truck bed ? N forward.

10. 8.

    A box on a truck bed speeds up with the truck and does not slip. What force accelerates it, Ren?

    • Static friction from the truck bed, pointing forward
    • The normal force from the bed, pointing forward
    • The force of the truck's motion carried over to the box
    • The box's inertia pushing it along with the truck
11. 9.

    The static friction coefficient between box and bed is 0.4. At what acceleration does the 10 kg box begin to slip, Tala?

    • About 9.8 m/s², the acceleration of free fall
    • About 39 m/s², the maximum friction force itself
    • About 0.4 m/s², the friction coefficient itself
    • About 3.9 m/s², whatever the box's mass
12. 10.

    A drone lifts a load up: speeding up, then at a steady speed, then slowing down. How does the cable's tension compare, Zee?

    • Largest when slowing down, since the drone works hardest to stop
    • The same in the three stages, since the load moves upward the whole time
    • Largest speeding up, middle at steady speed, smallest slowing
    • Largest at steady speed, since the load moves fastest then