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. 

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.

What was their lowest speed and when was this?