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Four vehicles travelled on a road with constant velocities. The car overtook the scooter at 12 o'clock, then met the bike at 14.00 and the motorcycle at 16.00. The motorcycle met the scooter at 17.00 then it overtook the bike at 18.00. At what time did the bike and the scooter meet?

### There and Back

Brian swims at twice the speed that a river is flowing, downstream from one moored boat to another and back again, taking 12 minutes altogether. How long would it have taken him in still water?

### Escalator

At Holborn underground station there is a very long escalator. Two people are in a hurry and so climb the escalator as it is moving upwards, thus adding their speed to that of the moving steps. ... How many steps are there on the escalator?

# Motion Sensor

##### Stage: 4 Challenge Level:

A motion sensor collects data. At regular intervals it records the distance between itself and an object. If that object is moving towards, or away from, the sensor the distance data will change. You might like to experiment with this simulation of a motion sensor .

For 20 seconds a motion sensor is collecting data as a person moves backwards and forwards in front of it.

Here's the distance-time graph for that movement. Can you describe the person's motion? (the units are metres and seconds)

When was the person moving quickest? Calculate an estimate for this speed.