$(a)$ Differentiate acceleration from velocity.
$(b)$ Can a body have acceleration without change in magnitude of velocity? Explain with an example.
$(c)$ $A$ motor boat starting from rest on a lake accelerates in a straight line at a constant rate of $3 \, m s^{-2}$ for $8 \, s$. How far does the boat travel during this time?

(C) Acceleration is the rate of change of velocity,whereas velocity is the rate of change of displacement.
$(b)$ Yes. In uniform circular motion,the magnitude of velocity (speed) remains constant,but the direction changes continuously. Since acceleration is a vector quantity,this change in direction results in centripetal acceleration.
$(c)$ Given: Initial velocity $u = 0 \, m s^{-1}$,acceleration $a = 3 \, m s^{-2}$,time $t = 8 \, s$.
Using the second equation of motion: $S = ut + \frac{1}{2}at^2$
$S = (0 \times 8) + \frac{1}{2} \times 3 \times (8)^2$
$S = 0 + \frac{1}{2} \times 3 \times 64$
$S = 3 \times 32 = 96 \, m$.
The boat travels $96 \, m$ during this time.