Question

How much pressure will man of weight 80kg f exert on the ground when (i) he is lying and (ii) he is standing on his feet ? Given that the area of the body of the man is 0.6m² and that of a foot is 80cm².

Answer 1

The pressure an 80 kg man exerts on the ground is 1306.67 Pa when lying and 49000 Pa when standing, calculated by dividing the force (weight) by the area of contact.

Step-by-step explanation:

The pressure exerted by a man on the ground depends on his weight and the area of contact. When the man is lying down, his weight is distributed over the larger area of his body, whereas when standing, the weight is concentrated on the smaller area of his feet. To calculate pressure: Pressure (P) = Force (F) / Area (A).

For an 80 kg man (weight = mg, where g is the acceleration due to gravity, about 9.8 m/s2), we can calculate the following:

1. When lying: F = 80 kg × 9.8 m/s2 = 784 N (Newtons). Given the body area of 0.6 m2, pressure P = 784 N / 0.6 m2 = 1306.67 Pa (Pascals).
2. When standing: The area of both feet is 2 × 80 cm2 = 160 cm2 = 0.016 m2. Therefore, P = 784 N / 0.016 m2 = 49000 Pa.

The pressure will be 1306.67 Pa when lying and 49000 Pa when standing.