How to find relative velocity?

Question

Two boats are observed from a coastguard station. They have the following displacements (s) and velocity vectors (V) with distances measured in kilometres and speeds in kilometres per hour.

S1=2i - 7j and v1=10i 10j at 10.00h

S2=4i - 6j and v2=i 3j at 10.30h

all i really want to know is how to find the first boats velocity and speed at the same time as the second boat and would it be at 10.30 aswell.?

Answer 1

Seems like relative velocity would be v1-v2,

and speed would be sqrt(i^2 + j^2)

Answer 2

It's assumed that the motions are linear uniform

Take 10 h as origin of time, the vector equation of boat 1 is

S(t) = S1 +v1.t

At 10.30 h (this is different from 10 h 30 mn which should be written as 10.5 h), t = 0.30 h

S(0.30) = S1 + 0.30 v1

Projections of that vector relation on x- and y- axes are

Sx = 2i + 0.30*10 = 2i + 3

Sy = -7j +0.30*10 = -7j + 3

Displacement  of boat 1 at 10.30 h is S (2i+3, -7j+3)

Answer 3

what are you going to do after finding it...?

Answer 4

call it and listen for the ringtone

Answer 5

too difficult