\(\frac{{{g_{planet}}}}{{{g_{earth}}}} = \frac{{{M_{planet}}}}{{{M_{earth}}}}{\left( {\frac{{{R_{earth}}}}{{{R_{planet}}}}} \right)^2}\)
\( = \frac{1}{{10}} \times {\left( {\frac{3}{1}} \right)^2} = \frac{9}{{10}}\)
\(H = \frac{{{u^2}}}{{2g}}\)
\(\frac{{{H_{planet}}}}{{{H_{earth}}}} = \frac{{{g_{earth}}}}{{{g_{planet}}}}\)
\({H_{planet}} = \frac{{10}}{9} \times {H_{earth}}\)
\( = \frac{{10}}{9} \times 90\)
\(= 100\, metre.\)