Answer: Ok, we can put the truck on a x-axis and the police car on the y-axis.
if the truck has a velocity of 30km/h and in an hour will be in the intersection, then it has a 30km distance to the intersection, who will be our 0 in our graph. so truck vector is (30km,0)
where a vector is of the form (x,y)
for the police car is the same, it has 40km distance to the intersection, but in the y-axis, so the vector is (0,40km)
so the vector representing the displacement of the truck with respect of the police car is the difference of both vectors
it is (30km, - 40km)
if you want a more precise, you can write the vector of the form
(30 km - 30km/h*t, 40 km - 40km/h*t) where t is time.
this second vectors takes in account how the position of the vehicles changes as the time goes.
