Question

AInteractive Solution 11.13 presents a model for solving this problem. A solid concrete block weighs 140 n and is resting on the ground. Its dimensions are 0.430 m Times 0.190 m Times 0.10 m. A number of identical blocks are stacked on top of this is one. What is the smallest number of whole bricks (including the one on the ground) that can be stacked so that their weight creates a pressure of at least two atmospheres on the ground beneath the first block?
Thank you!

Answer 1

Atmospheric pressure is Patm = 101325 N/m2

The pressure of a single block is Pb = 140 N / (.430m *.190m) = 1713.58 N/m2 (largest area flat on ground. more stable)

Therefore the number of blocks, N, that can be stacked up to create a pressure of at least 2Patm is N ≥ Patm/ Pb

[Comment: This may be a trick question, since there is already one atmospheric pressure present without any blocks; that is why I didn't use 2Patm to calculate N.]

N ≥ 101325/1713.58 =59.13

Therefore, N ≥ 59, at least 59 blocks are needed (since the atmosphere is still pushing on the top block).

Answer 2