M1 Vectors problem

Hi,

Could anybody tell me how I can deal with this vector problem?

A ship moves so that its position vector, in metres, relative to a lighthouse at time t seconds is:

$r = (80-0.4t)i +(2t-80)j$

THe first part of the question is to find the distance of the ship from the lighthouse when t = 60, which I've done (it's 68.8 metres).

But I'm not sure how to approach the second part:

Find the times when the ship is (i) due north of the lighthouse and (ii) north-east of the lighthouse.

I'm a bit stumped on this one, so any advice would be greatly appreciated!

Hi,

Could anybody tell me how I can deal with this vector problem?

A ship moves so that its position vector, in metres, relative to a lighthouse at time t seconds is:

$r = (80-0.4t)i +(2t-80)j$

THe first part of the question is to find the distance of the ship from the lighthouse when t = 60, which I've done (it's 68.8 metres).

But I'm not sure how to approach the second part:

Find the times when the ship is (i) due north of the lighthouse and (ii) north-east of the lighthouse.

I'm a bit stumped on this one, so any advice would be greatly appreciated!