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?
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?
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?
The person was moving quickest at the point where the graph's
slope or gradient, either up or down, is steepest.
Between 9 seconds and 12 seconds they walked 4 metres, so a
reasonable estimate for the speed can be found dividing the
distance by the time.
4 metres in 3 seconds gives an average of around 1.3 m/s
Average speeds for other parts of the motion can be estimated in
a similar way to give approximate speeds of 0.6 m/s, 0.5 m/s, then
the 1.3 m/s (fastest) and finally 0.25 m/s
If the person switches direction, say they were going forwards
and then go backwards, or the other way round, then there was an
instant when they stopped.
In this question that happened three times :
At around 9 seconds, 12 seconds and 16 seconds, the person
switched between motion forwards and motion backwards.