What is retardation?

$A$ body in one-dimensional motion has zero speed at an instant. At that instant,it must have:

The acceleration of a particle which moves along the positive $x$-axis varies with its position as shown in the figure. If the velocity of the particle is $0.8 \,ms^{-1}$ at $x=0$, then its velocity at $x=1.4 \,m$ is (in $ms^{-1}$)

$A$ body is moving with variable acceleration $a$ along a straight line. The average acceleration of the body in the time interval $t_1$ to $t_2$ is

The displacement equation for a particle is $s = 3t^3 + 7t^2 + 14t + 8 \ m$. Its acceleration at time $t = 1 \ s$ is ....... $m/s^2$.

The acceleration $(a)$ - time $(t)$ graph for a body starting from rest is given below. The maximum speed of the body is (in $m/s$)