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.

   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
4. 4.

   “Free-body diagram (example data):” Using the diagram, what is the block's acceleration down the ramp, Jun?

   • 4.9 m/s², from mg sin 30° alone
   • 2.45 m/s², half of g sin 30° because of the slope
   • 8.5 m/s², from g cos 30°, the part into the ramp
   • 9.8 m/s², the acceleration of free fall in the open

5. 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.

6. 5.

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

   • About 6.6 m/s² down the ramp, adding friction
   • 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
7. 6.

   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
   • Disagree: it balances only the weight's part into the ramp
   • 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
8. 7.

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

   • Disagree: it reads more only if the lift speeds up upward
   • Agree: moving upward adds to the person's weight on the scale
   • Disagree: the scale reads less when the elevator is moving up
   • Agree: the scale reads the elevator's speed times the mass
9. 8.

   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: lighter balls fall faster because they have less weight
   • Disagree: the extra pull is cancelled by the extra mass, so a = g

10. 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.

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