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Class 7 Science — Speed and motion

Work out speed, distance or time from the other two, choose between m/s and km/h, and tell uniform linear motion from non-uniform.

Name: ________________________

Before you start

A train leaves station A and reaches station D. Its position along the straight track is marked out below.

0120

Read the marks as the position of a train at equal intervals of time. When each gap between successive positions matches the one before, the speed is not changing and the motion is uniform. When the gaps grow or shrink, the speed is changing and the motion is non-uniform.

  1. 1.A train travels at a speed of 90 kilometres per hour. How many hours does it take to cover 360 kilometres? Answer with a number.

  2. 2.Two trains are timed over the same hour. Train X covers 20 kilometres in each ten-minute interval. Train Y covers 20, then 15, then 25. Which is in uniform linear motion, and how do you know?

    • a) Train Y, because its distances add up to the same total
    • b) Both, because both travel along a straight track
    • c) Train X, because it covers equal distances in equal intervals of time
    • d) Neither, because no real train holds one speed for long

  3. 3.What makes a motion uniform linear motion?

    • a) The object keeps to one speed, whatever path it takes
    • b) The object covers the same distance as another object in the same time
    • c) The object moves along a straight line, whatever its speed does
    • d) The object moves along a straight line at a constant speed

  4. 4.A runner covers 400 metres in 50 seconds. What is the runner's speed in metres per second? Answer with a number.

  5. 5.Three sprinters are part-way through a race on a straight track and one of them is ahead of the others. What does that tell you?

    • a) She has a longer stride, which is a different thing from speed
    • b) She has covered more distance in the same time, so she is the faster
    • c) She started before the others did
    • d) Nothing until the race is over

  6. 6.The chapter calls uniform linear motion an idealisation. Why?

    • a) Objects are seldom found holding a constant speed for long, which is why average speeds are used
    • b) It applies to trains but to nothing else
    • c) Straight tracks do not exist in practice
    • d) Speed cannot be measured accurately enough to check it

  7. 7.Sort each stretch of a train's journey along a straight track.

    Groups: Uniform linear motion · Non-uniform linear motion

    • A train covering the same distance in each ten-minute interval
    • A train pulling out of a station and picking up speed
    • A train covering different distances in successive ten-minute intervals
    • A train slowing down as it comes into a station
    • A train running at an unchanging speed along a straight stretch

  8. 8.A train covers 300 kilometres in 4 hours. What is its speed in kilometres per hour? Answer with a number.

Answer key — Class 7 Science — Speed and motion

  1. 1. 4
  2. 2. c) Train X, because it covers equal distances in equal intervals of time
  3. 3. d) The object moves along a straight line at a constant speed
  4. 4. 8
  5. 5. b) She has covered more distance in the same time, so she is the faster
  6. 6. a) Objects are seldom found holding a constant speed for long, which is why average speeds are used
  7. 7. A train covering the same distance in each ten-minute interval → Uniform linear motion; A train running at an unchanging speed along a straight stretch → Uniform linear motion; A train covering different distances in successive ten-minute intervals → Non-uniform linear motion; A train pulling out of a station and picking up speed → Non-uniform linear motion; A train slowing down as it comes into a station → Non-uniform linear motion
  8. 8. 75