Does a ball roll farther on grass or cement?

cement.

did you ever think of trying it?

.

Cement. To roll on grass, the ball has to bend and crush the grass. This requires energy. The energy is taken from the kinetic energy of the ball (=1/2 x m x v^2), so the ball slows down sooner.

Depends on how hard you roll it. If you roll it the same and it is the same ball, with the same amount of air, under the same conditions, then cement.