When landing after a spectacular somersault, a 35.0 kg gymnast decelerates by pushing straight down on the mat. calculate the force she must exert if her deceleration is 9.00 times the acceleration of gravity?

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,

Here, W is the weight of the gymnast and a is the acceleration experienced by the gymnast ( acceleration due to gravity)  

Therefore,

OR

Given and

Substituting these values in above formula and calculate the force exerted by the gymnast,