c
તકતીની જાડાઈ \(s \) માટે  \(v = (19/20)u\)

\({v^2}\, = \,\,{u^2}\,\, + \,\,2as\,\, \Rightarrow \,\,{\left( {\frac{{19}}{{20}}u} \right)^2}\,\, = {u^2}\, + \,\,2as\,\,\,\)

\( \Rightarrow \,\,2as\,\, = \,\,\left( {\frac{{361}}{{400}}} \right){u^2}\, - \,\,{u^2}\,\, \Rightarrow \,\,\,a\,\, = \,\, - \,\,\left( {\frac{{39}}{{400}}} \right)\,\,\,\frac{{{u^2}}}{{2s}}\,\) નો ઉપયોગ કરતાં 

ઓછામાઓછી \( n\)  તકતીઓ લેવામાં આવે તો \(\,\,{{\text{0}}^{\text{2}}}\,\, = \,\,{u^2}\, + \,\,2a\,(ns)\,\)

\(\, \Rightarrow \,\,n\,\, = \,\, - \,\,\frac{{{u^2}}}{{2as}}\,\, = \,\,\frac{{{u^2}}}{{2\left( {\frac{{39}}{{400}}} \right)\,\frac{{{u^2}}}{{2s}}\,\, \times \,\,s}}\,\, \approx \,\,10.26\)

ઓછામાં ઓછી તકતીઓની સંખ્યા \(= 11\)