Displacement and velocity, with a frame of reference

Answer Key - Grade 11 Science Worksheet - Challenge Me

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

1. 1.

   East is positive. At t = 0, Ari's cart A is at x = 0 moving 4 m/s; cart B is at x = 60 m moving -2 m/s. When do they meet?

   10 s
2. 2.

   East is positive. At t = 0, Bo's cart A is at x = 0 moving 7 m/s; cart B is at x = 54 m moving -2 m/s. When do they meet?

   6 s
3. 3.

   East is positive. At t = 0, Esme's cart A is at x = 0 moving 8 m/s; cart B is at x = 75 m moving 3 m/s. When do they meet?

   15 s

4. Read this first

   Cart position each second (example data)

   time (s)	position (m)
   0	0
   1	6
   2	8
   3	6
   4	0
   5	-10

5. 4.

   In the position table, when does the cart reverse direction, Jun?

   • At 0 s, when the cart starts moving
   • At 4 s, when x is back at 0 m, the origin
   • At 2 s, where x stops rising and starts falling
   • At 5 s, the last reading in the table
6. 5.

   A ship sails 40 km at 30° north of east, then 30 km due north. What is its displacement from the start, Kira?

   • 70 km, adding the two lengths
   • About 61 km, 35° north of east
   • 50 km north, ignoring the eastward part
   • About 61 km, 55° north of east
7. 6.

   A plane has an airspeed of 250 m/s. The wind blows 50 m/s toward the east. To fly due north, what heading and ground speed does Luz need?

   • Head 11.5° west of north; ground speed about 245 m/s
   • Head due north; ground speed about 245 m/s, drifting east
   • Head 78.5° west of north; ground speed about 245 m/s
   • Head 11.5° west of north; ground speed 250 m/s
8. 7.

   Milo says: "I drove 120 km in 2.0 h, so my average velocity was 60 km/h." The trip ended 30 km from the start. Find the flaw.

   • No flaw: speed and velocity mean the same thing here
   • The average velocity is 30 km/h, the distance from the start
   • The average velocity is 60 km/h, but the speed is 15 km/h
   • 60 km/h is the average speed; the average velocity is 15 km/h
9. 8.

   Noah says two cars at 60 km/h have equal velocities. One drives east, the other north. Judge the claim and find their relative velocity.

   • False: only the speeds match; relative velocity is 120 km/h
   • False: only the speeds match; relative velocity is about 85 km/h
   • True: both are 60 km/h, so the relative velocity is 0
   • False: only the speeds match; relative velocity is 60 km/h

10. Position each second (example data)

    time (s)	position (m)
    1	1
    2	4
    3	9
    4	16
    5	25

11. 9.

    Pia says the velocity at 3 s is 8 m/s, the slope from 3 s to 5 s in the position table. Judge the claim.

    • Supported: the slope from 3 s to 5 s is the velocity at 3 s
    • Not supported: the velocity at 3 s is about 7 m/s, from 3 s to 4 s
    • Not supported: the velocity at 3 s is 9 m/s, its position
    • Not supported: the velocity at 3 s is about 6 m/s; 8 m/s is later
12. 10.

    Tala rides a moving escalator up in 20 s, or walks up the stopped escalator in 30 s. How long to walk up the moving one?

    • 25 s, the average of 20 and 30
    • 50 s, the sum of 20 and 30
    • 12 s: the two rates add up
    • 10 s, the difference of 20 and 30