The chair has four cylindrical legs each with a diameter of

Question

Can someone please tell me why the area was divided by two for the chair? (see full problem below) (4π (0.015 / 2 m)²)

A 70 kg student stands on a 10 kg chair. The chair has four cylindrical legs each with a diameter of 0.015 m. What pressure does the student and chair exert on the ground?

Answer:

P = F / A

The force is the total weight, and the area is the total cross-sectional area of the four chair legs.

P = mg / (4 πr²)

P = (70 + 10 kg)(9.8 N/kg) / (4π (0.015 / 2 m)²)

P = 1.1x10⁶ Pa