A contractor is installing a metal roof system in Maui's hurricane zone. The roof area is 2,400 sq ft with an uplift pressure of 45 psf. What is the total uplift force that must be resisted?
Correct Answer
B) 108,000 lbs
Total uplift force = Area × Pressure = 2,400 sq ft × 45 psf = 108,000 lbs total uplift force to be resisted.
Why This Is the Correct Answer
The correct answer is 108,000 lbs. The calculation is straightforward: Total uplift force = Area × Pressure = 2,400 sq ft × 45 psf = 108,000 lbs. This is the fundamental formula for converting distributed pressure (pounds per square foot) into total force (pounds) acting on the entire roof surface.
Why the Other Options Are Wrong
Option A: 128,000 lbs
128,000 lbs results from using an incorrect pressure value, such as approximately 53 psf instead of 45 psf (2,400 × 53.3 ≈ 128,000). There is no basis for using 53 psf in this problem, making this a distractor based on arithmetic error.
Option C: 98,000 lbs
98,000 lbs would result from approximately 2,400 × 40.8 psf. If a candidate mistakenly uses 40 psf instead of 45 psf, they might get close to this figure (2,400 × 40 = 96,000). This reflects rounding or misreading the given pressure value.
Option D: 118,000 lbs
118,000 lbs would result from approximately 2,400 × 49 psf — again using a pressure not stated in the problem. This is a plausible-sounding distractor that catches candidates who second-guess the given values.
Memory Technique
Force = Area × Pressure. Think of it as 'how much pressure pushes on every single square foot, added up across the whole roof.' For this problem: 2,400 squares each pushing up with 45 lbs = 2,400 × 45 = 108,000 lbs. Double-check: 2,400 × 45 = 2,400 × 40 + 2,400 × 5 = 96,000 + 12,000 = 108,000.
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