Been doing a science report on an experiment to do with the crater sizes and if they increases due to the two variables of Velocity(changed the height), and Mass. I'm doing the Analysis and from my data I see that the width of the crater increases but after the height of 40cm, the marbles crater width decreases. Why is this, I thought there might be an error in the data collection or is it something more to do with physics.

what are you using as an impact medium.

if youre using sand, the reason could be because the sand is just falling back into the crater. i dunno, you could try a different medium.

overall, i think the factor in determining crater size is energy. to find kinetic energy,
E = 0.5*mass*(velocity^2)

also remember that in a dropping object is determined by acceleration, time or distance. use your kinematic equations for motion with constant acceleration.

Yeh I've included the equations and stuff, and i said that the decreses in crater size might be lack of experimental conditions control, like the sand not being flat, the way the marble being dropped had changed, so on, so on.