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, 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
2. 2.

   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

3. 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

4. 3.

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

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

   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, 55° north of east
   • 50 km north, ignoring the eastward part
   • About 61 km, 35° north of east
6. 5.

   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 60 km/h, but the speed is 15 km/h
   • 60 km/h is the average speed; the average velocity is 15 km/h
   • The average velocity is 30 km/h, the distance from the start
7. 6.

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

8. Position each second (example data)

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

9. 7.

   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.

   • Not supported: the velocity at 3 s is about 7 m/s, from 3 s to 4 s
   • Supported: the slope from 3 s to 5 s is the velocity at 3 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
10. 8.

    Rain falls straight down at 6.0 m/s. Ren cycles east at 8.0 m/s. What is the rain's speed relative to the cyclist, and its angle from the vertical?

    • 10 m/s, 53° from the vertical, coming from ahead
    • 10 m/s, 53° from the vertical, coming from behind
    • 10 m/s, 37° from the vertical, coming from ahead
    • 14 m/s, 53° from the vertical, coming from ahead
11. 9.

    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?

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

    Zee rides a train at a steady 20 m/s. A friend stands on the platform. Both watch the same falling ball. Which quantity do they measure the same?

    • Its displacement in 1 s, since the clock time is shared
    • Its acceleration: the frames differ by a steady velocity
    • Its velocity, since the ball is one object in both views
    • Nothing: each frame sees a different motion of the ball