# Rope clocks

1. Jun 2, 2004

### Gokul43201

Staff Emeritus
You have two cloth ropes. The ropes have non-uniform thicknesses and are of different lengths. You also have a bucket of colored liquid. When you dip an end of a rope into the liquid, the colored liquid wicks through the rope, progressing through it at some non-constant rate. The total wick-time for the ropes is 1 hour each. How would you measure 45 minutes using only the ropes and the liquid ?

2. Jun 2, 2004

Old puzzle.

3. Jun 2, 2004

### Gokul43201

Staff Emeritus
oops sorry...just ignore it. I'm fairly new here and haven't looked through all the older stuff.

4. Jun 6, 2004

### vikasj007

this puzzle might be old, but i would still like to know the answer.

5. Jun 6, 2004

### Gokul43201

Staff Emeritus
Sure thing : but let me give you a BIG hint instead. What happens when you simultaneously dip both ends of a rope in the liquid ?

6. Jun 16, 2004

### abertram28

im sure you just fold one in half and dip the ends in the water.

after its full, you can dip the other rope in two spots, and it will wick in 15 mins.

one semantic problem is that once a wicked part meets another wicked part the wicking rate wouldnt increase at the ends. the 15 minute timer wouldnt be exact.

7. Jun 16, 2004

### Gokul43201

Staff Emeritus
For closure on this...here's the solution :

START : Dip one end of rope 1 and both ends of rope 2. Rope 2 will wick through in 30 mins. So rope 1 has exhausted 30 mins of its length and has 30 mins of wick-time left. At the instant that rope 2 completes wicking through (after 30 mins), dip the other end of rope 1. So now a half-hour rope has liquid wicking through from both ends, and hence will last 15 mins.

TOTAL TIME = 30 +15 =45 mins exactly !

No probkem !