Originally Posted by

**jackiemoon** Hi,

Can anybody help with this problem please:

At 3pm the big hand of a clock is pointing at 12, and the small hand pointing at 3 (at right angles, obviously). The question is what time will it be when the hands are at right angles again for the first time?

This problem is driving me nuts. I know there's probably a very simple way to do it but it's eluding me at the moment. I have worked out position vectors and velocity vectors and i'm thinking that it's something to do with dot product equal to 0 and solving for t or else using the distance between the 2 position vectors being root 2 (assuming the clock radius is 1 unit).

Any suggestions? Apart from switching to a digital clock(Rofl)

Thanks