# Puzzles

## Superdog

A dog is running along a beach at 2m/s. The dog's owner blow a whistle every 10 seconds. Each time the dog hears a whistle, she doubles her speed. How many whistles will the dog hear?

(Hint: speed of sound = 343m/s)

(Hint 2: The answer is not eight!)

#### Show answer & extension

#### Hide answer & extension

On hearing the eighth whistle, the dog will be running at 512m/s, faster than the speed of sound. Hence, no more of the master's whistles will reach the dog. However, the dog will catch up with the seven whistles she has already heard and hear them again. So **fifteen** whistles will be heard in total.

#### Extension

How much time will the dog have been running for when she hears the final whistle?