A particle moves along a straight line such that its displacement s at any time t is zero is s=t^3-6t^2+3t+4 meters, t being in second. The velocity when acceleration is zero is

Hint. For velocity calculate ds/dt and for acceleration differentiate velocity.

Once you equate acceleration to 0, you will get t = 2s.

Put 't=2' in the obtained derivation for ds/dt, you will get the value of velocity.

 

Try.