The initial velocity of a particle is u (at t = 0 ) and the acceleration f  is given by at. Which of the following relation is valid 

• A

  $\mathrm{v}=\mathrm{u}+{\mathrm{at}}^2$

• B

  $\mathrm{v}=\mathrm{u}+\mathrm{a}\frac{{\mathrm{t}}^2}{2}$

• C

  $\mathrm{v}=\mathrm{u}+\mathrm{at}$

• D

  $\mathrm{v}=\mathrm{u}$