A particle moves along a straight line such that its displacement at any time t is given bys = t3-6t2+3t+4The velocity when its acceleration is zero, is

x = t3-6t2+3t+4Velocity v = dxdt= 3t2-6×2t+3×1+0                     = 3t2-12t+3Acceleration a = dvdt = 3×2t -12×1+0 = 6t-12Acceleration is zero at time t given by 6t-12 = 0⇒ t = 2 secondsSo, velocity v at t = 2 seconds isv = (3t2-12t+3)t = 2s   = 3 ×(2)2-12×2+3 =-9 m/s