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Question

A submarine is designed to withstand an absolute pressure of $100 \text{ atm}$. How deep can it go below the water surface?
(Consider the density of water = $1000 \text{ kg m}^{-3}$, $1 \text{ atm} = 1 \times 10^5 \text{ Pa}$ and gravitational acceleration $g = 10 \text{ m/s}^2$)

This question was previously asked in
NEET UG Re-Exam 2026 Question Paper (21-Jun-2026)
The correct answer is
$990 \text{ m}$

Submarine Depth Calculation: Pressure Analysis

The problem asks for the maximum depth a submarine can reach based on its tolerance to absolute pressure.

Key Information Provided

  • Maximum Absolute Pressure ($P_{abs\_max}$) the submarine can withstand: $100 \text{ atm}$
  • Density of water ($\rho$): $1000 \text{ kg m}^{-3}$
  • Atmospheric pressure conversion: $1 \text{ atm} = 1 \times 10^5 \text{ Pa}$
  • Gravitational acceleration ($g$): $10 \text{ m/s}^2$
  • Assume standard atmospheric pressure at the surface ($P_{atm}$): $1 \text{ atm} = 1 \times 10^5 \text{ Pa}$

Calculating Maximum Depth

The absolute pressure ($P_{abs}$) at a certain depth ($h$) in water is given by the formula:

$P_{abs} = P_{atm} + \rho g h$

First, convert the maximum withstandable pressure to Pascals:

$P_{abs\_max} = 100 \text{ atm} \times (1 \times 10^5 \text{ Pa / atm}) = 1 \times 10^7 \text{ Pa}$

Now, set the absolute pressure equal to the maximum withstandable pressure and solve for depth ($h$):

$1 \times 10^7 \text{ Pa} = (1 \times 10^5 \text{ Pa}) + (1000 \text{ kg m}^{-3}) \times (10 \text{ m/s}^2) \times h$

Subtract the atmospheric pressure from the maximum absolute pressure:

$P_{water} = P_{abs\_max} - P_{atm}$ $P_{water} = (1 \times 10^7 \text{ Pa}) - (1 \times 10^5 \text{ Pa})$ $P_{water} = 10000000 \text{ Pa} - 100000 \text{ Pa} = 9900000 \text{ Pa}$

This remaining pressure is due to the water column. Use the formula $P_{water} = \rho g h$ to find $h$:

$9900000 \text{ Pa} = (1000 \text{ kg m}^{-3}) \times (10 \text{ m/s}^2) \times h$ $9900000 = 10000 \times h$

Solve for $h$:

$h = \frac{9900000}{10000}$ $h = 990 \text{ m}$

Therefore, the submarine can go $990 \text{ m}$ deep.

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