Explanation:
We know that \(s = ut + \frac{1}{2}a{t^2}\)
\(5 = \left[ {u\,(1) + \frac{1}{2}a{{(1)}^2}} \right] - 0\,\,\,\,\,\,\,\,\,\,\,\,\,(1)\)
\(2 = \left[ {u(3) + \frac{1}{2}a{{(3)}^2}} \right] - \left[ {u\,(2) + \frac{1}{2}a{{(2)}^2}} \right]\)
\(2 = u(3 - 2) + \frac{1}{2}a\,({3^2} - {2^2})\,\,\,\,\,\,(2)\)
\((1)\,\, - \,\,(2)\)
\( \Rightarrow \,\,\,3 = \frac{a}{2}[1 - 5] \Rightarrow a = \frac{{ - 6}}{4}\)
\( \Rightarrow \,\,\,F = ma = - \,6N({\rm{retarding}}\,{\rm{force)}}\)