1. The problem statement, all variables and given/known data A particle is located at r=(2i+4j)m at t=0s. At t=3s it is at r=(8i-2j)m and has velocity v=(5i-5j)m/s a)what is the particles acceleration vector a? 2. Relevant equations r1=r0+v0(t1-t0)+1/2a(t1-t0)^2 v1=v0+at 3. The attempt at a solution v1=v0+at (5i-5j)m/s=v0+a(3s-0s) v0=(5i-5j)m/s-3a this is where i have trouble: I understand how my text uses this equation i just dont know were they got these numbers: r1=r0+v0(t1-t0)+1/2a(t1-t0)^2 (4i-4j)m=(3s^2)a+(2s)vo --> did they assume that r0=0? and how did they get r1? and where did they get 2sv0 because from the information given i thought it was all 3seconds okay well anyway i understand they would take the v0 found in the first part and sub it in to get this: (3s^2)a+ (2s)[(5i+5j)m/s - 3s(a)] =(4i+4j)m and a=(2i+2j)m/s^2 Please can someone explain to me where they got the 2 from and also i dont understand how they subtract3s(a) I would really appreciate it.