Physics pressure

Question

A solid concrete block weighs 169N and is resting on the ground. Its dimensions are .4mX.2mX.1m. A number of identical blocks are stacked on top of this one. What is the smallest number of whole blocks (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 P_atm = 101325 N/m²  

 

The pressure of a single block is P_b = 169 N / (.4mx.2m) = 2112.5 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 2P_atm  is N ≥ P_atm/ P_b 

 

[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 2P_atm to calculate N.]  

 

N ≥ 101325/2112.5 =47.96 

 

Therefore, N ≥ 48, at least 48 blocks are needed (since the atmosphere is still pushing on the top block).