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.

   Ari pulls a 10 kg wagon with 50 N at 37° above the ground. The sliding friction coefficient is 0.2. To 0.01 m/s², what is its acceleration?

   2.63 m/s²
2. 2.

   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
3. 3.

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

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

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

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

   • Disagree: the normal force is larger than the weight on a ramp
   • Agree: the surface always pushes back with the full weight
   • Agree: the ramp's tilt changes the weight but not the normal force
   • 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?

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

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

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

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?

    • The force of the truck's motion carried over to the box
    • The normal force from the bed, pointing forward
    • The box's inertia pushing it along with the truck
    • Static friction from the truck bed, pointing forward
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 3.9 m/s², whatever the box's mass
    • About 0.4 m/s², the friction coefficient itself
    • About 9.8 m/s², the acceleration of free fall
    • About 39 m/s², the maximum friction force itself
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?

    • 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
    • Largest when slowing down, since the drone works hardest to stop