The force applied to the cannonball and cannon is equal. The explosion inside the cannon will generate a pressure which will turn into a force on both cannonball and cannon. The cannon being heavier and fixed to the ground will move a bit, but the cannonball will be thrown away, fired.
<em><u>This</u></em><em><u> </u></em><em><u>it</u></em><em><u> </u></em><em><u>you</u></em><em><u> </u></em><em><u>can</u></em><em><u> </u></em><em><u>do</u></em><em><u> </u></em><em><u>it</u></em><em><u> </u></em><em><u>boy</u></em><em><u> </u></em><em><u>or</u></em><em><u> </u></em><em><u>girl</u></em><em><u> </u></em>
Volumetric cylinders and volumetric flasks