Calculate the pressure that a man of weight 70 kgf will exert on ground.
(a) When he is standing on feet.
(b) When he is lying on the ground.
The are of foot is `70cm^(2)` and area of his body is `0.5 m^(2)`.

Answer

To solve the problem, we will calculate the pressure exerted by a man weighing 70 kgf in two different scenarios: when he is standing on his feet and when he is lying on the ground.

### Given Data:
- Weight of the man (W) = 70 kgf
- Area of foot (A1) = 70 cm²
- Area of body when lying down (A2) = 0.5 m²

### Step 1: Convert Weight from kgf to Newtons
1 kgf is equivalent to 9.81 N. Therefore, we can convert the weight of the man to Newtons:
\[ W = 70 \, \text{kgf} \times 9.81 \, \text{N/kgf} = 686.7 \, \text{N} \]

### Step 2: Convert Area of Foot from cm² to m²
The area of the foot is given in cm². We need to convert it to m²:
\[ A1 = 70 \, \text{cm}^2 = 70 \times 10^{-4} \, \text{m}^2 = 0.007 \, \text{m}^2 \]

### Step 3: Calculate Pressure When Standing on Feet
Pressure (P) is defined as force (F) divided by area (A):
\[ P1 = \frac{F}{A1} \]
Substituting the values:
\[ P1 = \frac{686.7 \, \text{N}}{0.007 \, \text{m}^2} = 98096.43 \, \text{N/m}^2 \]
Rounding this to two decimal places gives:
\[ P1 \approx 98100 \, \text{N/m}^2 \]

### Step 4: Calculate Pressure When Lying on the Ground
In this case, the area (A2) is given as 0.5 m². We will calculate the pressure again using the same formula:
\[ P2 = \frac{F}{A2} \]
Substituting the values:
\[ P2 = \frac{686.7 \, \text{N}}{0.5 \, \text{m}^2} = 1373.4 \, \text{N/m}^2 \]

### Final Answers:
(a) Pressure exerted when standing on feet: **98100 N/m²**
(b) Pressure exerted when lying on the ground: **1373.4 N/m²**