A particle moving along x-axis has acceleration f, at time t, given by ${\text{f=f}}_0\left(1-\frac{\mathrm{t}}{\mathrm{T}}\right)$, where f₀ and T are constants. The particle at t = 0 has zero velocity. In the time interval between t = 0 and the instant when f=0, the particle’s velocity (v_x) is