Draw free-body diagrams and find the net force

Answer Key - Grade 11 Science Worksheet

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

1. 1.

   A drone's cable pulls a 2 kg box upward with 30 N. With g = 9.8 m/s², what is the box's acceleration, Ari?

   5.2 m/s²
2. 2.

   The scale reads 720 N. Using the diagram, what is the elevator's acceleration, Jun?

   • 2.2 m/s² upward
   • 12 m/s² upward, from 720 ÷ 60
   • 2.2 m/s² downward, since the scale reads high
   • 0 m/s², since the scale and weight are equal

3. Read this first

   Free-body diagram (example data)

   The lower of two stacked boxes on a table of mass 5 kg, with arrows from its center: weight 49 N down; push from the upper box (3 kg) 29.4 N down; normal force from the table ? N up.

4. 3.

   The boxes are at rest. What is the table's normal force on the lower box, Kira?

   • 78.4 N, the weight of both boxes
   • 19.6 N, the difference of the two
   • 29.4 N, the push from the upper box
   • 49 N, the weight of the lower box
5. 4.

   The box stays on the floor. Using the diagram, what is the normal force, Luz?

   • 21.9 N, from 39.2 minus 20 cos 30°, about 17.3 N
   • 39.2 N, the same as the box's weight on a level floor
   • 49.2 N, the weight plus the pull's upward part of 10 N
   • 29.2 N, since the pull's upward part lifts some weight
7. 5.

   Three ropes pull a ring: 6 N east, 10 N north and 2 N west. What is the size of the net force, Milo?

   • About 18 N, from 6 + 10 + 2
   • About 10.8 N
   • About 11.7 N, from √(6² + 10²)
   • About 12.8 N, from √(8² + 10²)
8. 6.

   In which direction is the net force on the ring, Noah?

   Use the picture in question 5.

   • About 68° north of east
   • About 31° north of east, from the ropes' average
   • About 22° north of east, from tan θ = 4 ÷ 10
   • About 59° north of east, if the 2 N west rope is ignored
9. 7.

   “a 2 kg ring pulled by three ropes of mass 2 kg” The ring has mass 2 kg. What is its acceleration, Pia?

   • About 2.7 m/s², from net force over twice the mass
   • About 5.4 m/s²
   • About 10.8 m/s², the net force alone
   • About 21.6 m/s², from net force times mass
10. 8.

    A 4 kg block slides at 6 m/s on a table with sliding friction coefficient 0.3. How does it stop, Ren?

    • After about 2.0 s, slowing at 2.9 m/s²
    • After about 20 s, slowing at 0.3 m/s²
    • After about 0.5 s, slowing at 11.8 m/s²
    • After about 4.1 s, slowing at 1.5 m/s²
11. 9.

    A 2 kg drone has 20 N of lift. With g = 9.8 m/s², what does it do, Tala?

    • It speeds up upward at 10 m/s², from 20 ÷ 2
    • It rises at a steady 0.2 m/s
    • It hovers, since the lift almost equals the weight
    • It speeds up upward at 0.2 m/s²
12. 10.

    A skydiver falling at a steady speed opens the parachute and draw a line jumps well above the weight. What happens next, Zee?

    • The diver keeps the same speed, since the speed was steady
    • The net force points up, so the diver slows down
    • The diver shoots upward, since drag now beats gravity
    • The diver stops at once, since drag is larger than weight