The displacement of a particle starting from rest at t = 0 is given by $\mathrm{s} = 9{\mathrm{t}}^2 – 2{\mathrm{t}}^3$. The time in seconds at which the particle will attain zero velocity is

According to the question, 

s = 9t² - 2t³ 

V =$\frac{ds}{dt}=$ 18t - 6t² 

if V = 0, then  18t - 6t²  = 0 ------ equation 1

by solving the equation 1 we get, 

t = 0 sec and t = 3 sec

Therefore the particle will attain zero velocity at the time of 3seconds