The first step id to find the decelleration of the foot ball when it is caught.
To do so, use this formula:
v = 0 m/s
Vo= 10 m/s
t = .02 s
Plug these values you know into the formula and you should get:
-500 m/s^2
Now plug this into the Force formula:
where m = .5 kg
You should get 250 N as your force.
Now, finally, for question A) , Impulse is equal to the force times the change in time, or:
Youre F = 250 N and your time = .02s
Therefore, the Impulse should be 5 N*s (Newton seconds)
For B)
see the work done to find the force, that should be your answer: 250 N.
HOPE THIS HELPS. PLEASE LET ME KNOW.