The displacement of a body of mass 10kg moving on a smooth horizontal surface is given by s=t44. The work done in first 2 seconds is
126J
420J
320J
520J
s=t44⇒v=t3----(1) ds=t3dt----(2) a=3t2W=∫Fds=∫mads=∫02 m3t2t3dtW=10×3∫02 t5dt =30×t6602=5×64=320J