A tennis ball is dropped on to the floor from a height of \( 9.8 \, \text{m} \). It rebounds to a height \( 5.0 \, \text{m} \). Ball comes in contact with the floor for \( 0.2 \, \text{s} \). The average acceleration during contact is ______ \( \text{ms}^{-2} \). (Given \( g = 10 \, \text{ms}^{-2} \))
