Penguins on a Plank
Twenty penguins, one plank, and a great deal of turning around.
A plank stretches twenty metres out over the water. One penguin stands at the very near end, at the 0 metre mark, facing up the plank. Nineteen more are scattered along it, some facing left, some facing right.
- Every penguin walks at one metre per second.
- When two penguins bump into each other, both turn around at once and keep walking. No time is lost.
- A penguin who reaches either end walks off, and is gone.
How long until the plank is empty?
It looks like it should depend on where everyone is standing, and on how much bouncing happens. Scatter them a few different ways and see whether it does.
Part one
Run it
One penguin is fixed at the near end, facing up the plank. Scatter the other nineteen, or click the plank to place them yourself — click a penguin you have placed to turn it round.
Then send them off, and watch the clock rather than the penguins.
05101520
Click the plank to add one facing0 of 19 placed
Elapsed0.0 s
Still on the plank1
Nineteen penguins still to place.