A rubber ball of mass $50g$ falls from a height of $1m$ and rebounds to a height of $0.5m$. Find the impulse and the average force between the ball and the ground if the time for which they are in contact was $0.1s$
The way it was solved in my book, they worked out the final velocity for each case (upward and downward motion of the ball) and finally determined the change in momentum. Once the impulse was out, the average force was resolved. My question is: As the ball was acting under the force of gravity, so it hits the ground with force $F=mg$; the ground should react with the same force, so can't we just multiply $g$ and given mass of the body to find $F$?