A particle starts from rest, accelerates at 2m/s² for 10 s and then goes for constant speed for  30 s and then decelerates at 4m/s² till it stops. What is the distance travelled by it?

Velocity acquired by body in 10 sec V= 0 + 2 × 10 = 20m/s.
And distance travelled by it in 10sec   $S_1=\frac{1}{2}\times 2{\left(10\right)}^2=100m$
Then it moves with constant velocity 20m/s for 30sec.
S2 = 20 × 30 = 600m
After that due to retardation 4m/s2 it stops  $S_3=\frac{v^2}{2a}=\frac{{\left(20\right)}^2}{2\times 4}=50m$
Total distance travelled is S1+S2+S3 = 750m