Answer
$\frac{6V}{5}$
Work Step by Step
Please see the attached image first.
Here, this question asked the average speed, and let's write the equation for average speed as follows.
$$Average\space speed= \frac{Total\space displacement}{Total\space time}-(1)$$
From equation (1) and the notations in the attached image, we can write,
$Average\space speed=\frac{S}{t1+t2}-(2)$
To find this value we have to find t1, and t2 in terms of S. Let's consider the figure (1) and apply equation $S=Ut+\frac{1}{2}at^{2}$ to the object.
$\rightarrow S=Ut+\frac{1}{2}at^{2}$
$\frac{S}{3}=2Vt1+\frac{1}{2}(0)(t1)^{2}$
$t1=\frac{S}{6V}$
Let's consider figure (2) and apply equation $S=Ut+\frac{1}{2}at^{2}$ to the object.
$\rightarrow S=Ut+\frac{1}{2}at^{2}$
$\frac{2S}{3}=Vt2+\frac{1}{2}(0)(t2)^{2}$
$t2=\frac{2S}{3V}$
$(2)\space=\gt$
$Average\space speed=\frac{S}{t1+t2}=\frac{S}{\frac{S}{6V}+\frac{2S}{3V}}=\frac{6V}{5}$
