physcis

How long does you hair grow each year? This is just an estimation and it will be nothing more than a reasonable guess.

If you make this guess... then it is easy to figure out how much it grows in a day-- then an hour-- than a second.

Just make the initial guess (year). You teacher doesn't care about how correct this guess is.

Then do the calculations down to second. Your teacher does care about the calculations.

2mm - 3 mm a week, guessing by how often I get a hair cut once it has grown about 15mm - 20mm (i.e. every 4 - 6 weeks).

The hair on my head now grows slower than that.
The hair on my back grows faster than that.

Aging is no fun.