# Maths edexcel a level question mechanics

Hi please can I have help with this question:

A particle P is moving with constant velocity. The position vector of P at time t seconds (t 0) is r metres, relative to a fixed origin O, and is given by
r = (2t 3)i + (4 5t)j
(a) Find the initial position vector of P.
The particle P passes through the point with position vector
(3.4i 12j)m at time T seconds.
(b) Find the value of T.
(c) Find the speed of P.
I know how to work out part a but I’m stuck on part b as I’ve tried substituting known values into the
Rt=R0 + vt equation but I still can’t figure it out.
Just pick either the i or j coordinate and solve for t so something like
4 - 5t = -12
at t= 0 you know the position
at t= T you know the position by r.

so, calculate displacement (in i, j directions) at t=T by using the above

you can also calculate corresponding displacements using position at t=0 and by(3.4i 12j)

the corresponding displacements must be what?
Original post by mqb2766
Just pick either the i or j coordinate and solve for t so something like
4 - 5t = -12

Thanks! I realise my mistake now
Original post by mathcool
at t= 0 you know the position
at t= T you know the position by r.
so, calculate displacement (in i, j directions) at t=T by using the above
you can also calculate corresponding displacements using position at t=0 and by(3.4i 12j)
the corresponding displacements must be what?

Thanks!