Answer :
The deceleration experienced by the gymnast is the 9 times of the acceleration due to gravity.
Now from Newton`s first law, the net force on gymnast,
[tex]F_{net} =F-W=ma[/tex]
Here, W is the weight of the gymnast and a is the acceleration experienced by the gymnast ([tex]9\times g[/tex] acceleration due to gravity)
Therefore,
[tex]F= ma+W[/tex] OR [tex]F=ma+mg=m(g+a)[/tex]
Given [tex]m = 30 kg[/tex] and[tex]a=9\times g=9\times 9.8 m/s^{2} =88.2 m/s^{2}[/tex]
Substituting these values in above formula and calculate the force exerted by the gymnast,
[tex]F=(40 kg) (88.2 m/s^{2} +9.8 m/s^{2} )[/tex]
[tex]F=3.537\times10^{3}N[/tex]