Physics > Mechanics > Motion In A Straight Line And Plane

A particle is moving in one dimension (along $x$ axis) under the action of a variable force. Its initial position was 16 m right of origin. The variation of its position ($x$) with time ($t$) is given as $x = -3t^3 + 18t^2 + 16t$, where $x$ is in m and $t$ is in s. The velocity of the particle when its acceleration becomes zero is ________ m/s.