When a block of mass m is kept on a surface of area A = 15 cm², the weight acts on the surface, resulting in a pressure P.
Force = m g = P * A
m = 1000 Pa * 15 *10⁻⁴ m² / 10 m/sec²
= 0.15 kg
The block rests now on a smaller surface area. So the weight of the block = m g acts (is spread) on the new surface area =>
Pressure = 0.15 kg * 10 m/s² / [ 10 * 10⁻⁴ m² ]
= 1, 500 Pa