Question

You and your friends are playing in the swimming pool with a 60-cm-diameter beach ball. How much force would be needed to push the ball completely under water?

Answer 1

The force must be equal to the buoyancy force:

$$F=\rho gV=\rho g\dfrac16\pi d^3,\\\space\\ F=1000·9.8·\dfrac16·3.14·0.6^3=1108\text{ N}.$$