A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. What amount of force acted on the ball?

Newton taught us that    Force = (mass) x (acceleration)Force  =  (0.2) x (20) = 4 newtons .Something to think about:  The ball can only accelerate while the club-face is in contact with it.  Once the ball leaves the club, it can't accelerate any more, because the force against it is gone.