Exams › JEE Main › Physics
The mass of a hydrogen molecule is 3.32×10⁻²⁷ kg. If 10²³ hydrogen molecules strike, per second, a fixed wall of area 2 cm² at an angle of 45° to the normal, and rebound elastically with a speed of 10³ m/s, then the pressure on the wall is nearly:
- 2.35 × 10³ N/m²
- 4.70 × 10³ N/m²
- 2.35 × 10² N/m²
- 4.70 × 10² N/m²
Correct answer: 2.35 × 10³ N/m²
Solution
Only the normal momentum component reverses: per molecule dp = 2mv cos45. Force = N*2mv cos45 = 1e23 * 2 * 3.32e-27 * 1e3 * 0.707 = 0.4695 N. Pressure = F/A = 0.4695 / 2e-4 = 2.35e3 N/m^2.
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