Figure $1$

$3.$ How do you work out the total force on a plane surface? From where the point of action is measured? How is the moment $M$ defined $($with reference to where is $M$ calculated$)?$

$4.$ How do you work out the forces on a curved surface?

$5.$ What is buoyancy$/$upthrust$?$ How does it come about?

$6.$ Refer to Figure $1.$ At where the square object is placed the upthrust is equal to the weight of the square. If you push the square to the bottom of the tank, will it stay at the bottom or come back to its original position? Explain why.

$7.$ A boat made of steel can float in water. How is it possible?