matter

some more simple doubts-
1)find maximum excess pressure inside a thin walled steel tube of radius R and thickness r(<< R) so that tube wont rupture(breaking stress of steel s)
2)a beaker containing water is rigidly fixed to platform.both are falling freely in vertical downward direction.level of water is h and base area a.assuming no water comes out what is the force exerted by water on bottom surface of beaker.(atm pressure p_o).
3)a block partially immersed in a liq and vessel containing it is moving up with acc a.it is obs by 2 observers one at rest and another acc upward with acc a.total buoyant force on block is more for which obs?