First convert Ht in meters

1ft=.3m

10.5 ft = 3.15m

we know H =

\(\displaystyle{u}^{{2}}{\frac{{{{\sin}^{{2}}{\left(\theta\right)}}}}{{{2}{g}}}}\)

\(\displaystyle{u}^{{2}}={\frac{{{2}{g}{H}}}{{{{\sin}^{{2}}{\left(\theta\right)}}}}}\)

\(\displaystyle{u}=\sqrt{{{\frac{{{2}{g}{H}}}{{{{\sin}^{{2}}{\left(\theta\right)}}}}}}}\)

H = 3.15 m g = 9.8m/s/s ? = 52.3

We will get

u=9.93 m/s

1ft=.3m

10.5 ft = 3.15m

we know H =

\(\displaystyle{u}^{{2}}{\frac{{{{\sin}^{{2}}{\left(\theta\right)}}}}{{{2}{g}}}}\)

\(\displaystyle{u}^{{2}}={\frac{{{2}{g}{H}}}{{{{\sin}^{{2}}{\left(\theta\right)}}}}}\)

\(\displaystyle{u}=\sqrt{{{\frac{{{2}{g}{H}}}{{{{\sin}^{{2}}{\left(\theta\right)}}}}}}}\)

H = 3.15 m g = 9.8m/s/s ? = 52.3

We will get

u=9.93 m/s