# Homework Help: Vectors and velocity

1. Jul 30, 2012

### phospho

In this question the unit vectors i and j are due east and north respectively and position vectors are given with respect to a fixed origin O.

A ship S is moving with constant velocity (2i−3j) km h−1 and a ship R is moving with constant velocity 6i km h−1.

a Find the bearing along which S is moving.

At noon S is at the point with position vector 8i km and R is at O. At time t hours after noon, the position vectors of S and T are s km and r km respectively.

b Find s and r, in terms of t.

At time T hours, R is due north-east of S. Find

c the value of T,

d the distance between S and R at time T hours.

I need help with part c)

Answer to a) 56.3, b) s=8i+(2i−3j)t - r=6ti

For part c i'm confused; if R is due south east of S, would it not mean the i and j components would be the same? Well it's wrong and if I do go on to equate the i and j components then I get T = 2, which is incorrect - the right answer is T = 8.

Cheers

2. Jul 31, 2012

### ehild

R is due north-east of S. The i and j components of what are equal?

ehild

3. Jul 31, 2012

### phospho

S and R I think