A particle P P\,P travels along a straight line through a point O O\,O so that at time t t\,t s after passing through O O\,O its displacement from O O\,O is x x\,x m, where x=t3−15t2+62tx = t^3 - 15t^2 + 62tx=t3−15t2+62t
the initial velocity of PPP,
the value of t t\,t for which P P\,P has zero acceleration.