Speed, velocity and distance-time graphs

Answer Key - Grade 8 Science Worksheet - Building Confidence

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

1. 1.

   Ari graphs a scooter rolling at a steady speed. Use the two marked points. What is the scooter's speed?

   4 m/s
2. 2.

   Bo rolls a ball along a track and graphs it. Use the two marked points. What is the ball's speed?

   5 m/s
3. 3.

   Esme's toy car rolls at a steady speed across the gym. Use the two marked points. What is the car's speed?

   6 m/s
4. 4.

   Both runners keep a steady pace. Jun times two runners and lists their distances from the start. Which statement does the table support?

   • The runners cannot be compared, because they began at different distances from the start
   • Runner A is faster: its distance grows 4 m each second, while B's grows 2 m each second
   • Runner B is faster: its distance from the start is larger than A's at each time listed
   • The two runners have the same speed: both distances keep growing at a steady rate
5. 5.

   Distance is measured from the start. Luz records three objects. Which two have the same speed?

   • No two of them can match, since the objects start at different distances from the start
   • H and J: both start at 30 m from the start, so they must move at the same speed
   • G and H: each one gains 10 m every 5 s, even though H starts 30 m farther along
   • The three objects have equal speeds, since each distance keeps growing as time passes

6. Read this first

   Cart on a straight track (example data)

   time (s)	position (m east of the start)
   0	12
   2	6
   4	0
   6	−6

7. 6.

   East is positive. Milo tracks a cart on a straight track. What is the cart's velocity?

   • −6 m/s: the position falls by 6 m between each pair of readings
   • 3 m/s east: the position changes by 3 m each second, so the cart moves east
   • −18 m/s: the position falls by 18 m from the first reading to the last
   • −3 m/s: the cart moves 3 m toward the west each second, so its velocity is negative

8. Toy helicopter (example data)

   time (s)	height (m)
   0	10
   2	16
   4	12
   6	6

9. 7.

   Up is positive. Pia flies a toy helicopter. What is its velocity from 4 s to 6 s?

   • −6 m/s: the height falls by 6 m between the two readings at 4 s and 6 s
   • −3 m/s: the helicopter descends 3 m each second, so its velocity is negative
   • +3 m/s: the height changes by 3 m each second, so the helicopter rises
   • +6 m/s: the helicopter climbed 6 m between the first two readings, so that is its velocity
10. 8.

    Ren walks 30 m east to a mailbox, then 30 m back west to the start, in 40 s. Which description is correct?

    • Distance 0 m, displacement 0 m, average speed 0 m/s
    • Distance 60 m, displacement 60 m, average speed 1.5 m/s
    • Distance 60 m, displacement 0 m, average speed 0 m/s
    • Distance 60 m, displacement 0 m, average speed 1.5 m/s
11. 9.

    Tala runs one 400 m lap of a track in 80 s and ends back at the start. Which statement is true?

    • The displacement is 400 m, so the average velocity is 5 m/s in the direction of the run
    • The average speed is 5 m/s, but the average velocity is 0 m/s
    • The average speed and the average velocity are both 5 m/s
    • The average speed is 0 m/s, since the runner ends at the starting line
12. 10.

    Zee bikes 50 m north, then 20 m south, along a straight street. What is the bike's displacement?

    • 30 m north, the net change from the start of the ride to its end
    • 70 m north, the total length of the whole path of the bike
    • 50 m north, the length of the first part of the ride, not the net change
    • 20 m south, the length of the last part of the ride, not the net change