function vars = constForce(t,vars_o,a)
%vars = constForce(t,vars_o,a);
% calculate position and velocity of a particle
%      t --> time (can be a vactor)
% vars_o --> vector of veariables as [x_o v_o]
%      a --> acceleration parameter

vars = [
    1/2*a*t^2 + vars_o(2)*t + vars_o(1)
    a*t + vars_o(2)
    ];

return