Question

Three boxes of equal dimensions (20 cm x 30cm x 50 cm), containing material which density 6.8x10-2 g/cm3 are to be stored for winter. What is the least amount of pressure that can be exerted by the blocks?
a) 1999.2 g/cm.s2
b) 40 Pa
c) 666 Pa
d) 4000 g/cm.s2
e) 333 Pa

Answer 1

Mass of the one block:

$$m = \rho V$$

Volume of one block:

$$V = S*h$$

According to the condition:

$$h = 50cm = 0.5m$$

Pressure force:

$$F = P = mg$$

Respectively:

$$F = P = \rho Vg = \rho Shg$$

Determine the pressure:

$$p = F/S = {\rho Shg \over S} = \rho gh$$

We obtain the initial formula for calculating the pressure:

$$p = 68(kg/m^3)*9.8(N/kg)*0.5(m) = 333.2(N/m^2) = 333.2(Pa)$$

$$333.2Pa \approx 333Pa$$

Answer: e) 333 Pa