4. O/N 15/P11/Q11 A block of weight 900 N has rectangular faces. The diagram shows the lengths of the sides
PoE
0.30 m
0.40 m
0.50 m
The block can rest on any of its faces. What is the minimum pressure that the block can exert on the ground when resting
on one of its faces?
A 900 Pa
B 4500 Pa
с 6000 Pa
D 7500 Pa

B) 4500 Pa

Explanation:

As pressure is force per unit area,

P = F/A

It stands to reason that the smallest pressure for a given force is when it is shared by the largest area.

The possible areas are

0.30(0.40) = 0.12 m²

0.30(0.50) = 0.15 m²

0.40(0.50) = 0.20 m²

The pressure when the face with the largest area (0.20 m²) is down is

P = 900 / 0.20 = 4500 N/m² or 4500 Pa

the other possible pressures would be

900/0.15 = 6000 Pa

900/0.12 = 7500 Pa

which are both larger than our solution.

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snell's law

refractve index = sin incidence / sin refraction