Granite has a mass density of 2650 kg/m3. Find its weight density in lb/ft3.
The Correct Answer and Explanation is:
To convert the mass density of granite (given in kg/m³) to weight density in lb/ft³, we follow these steps:
Given:
- Mass density of granite = 2650 kg/m³
- 1 kg = 2.20462 pounds (lb)
- 1 m³ = 35.3147 ft³
- Weight density = mass density × gravitational acceleration (9.81 m/s²)
- 1 N = 0.224809 lb
Step 1: Convert mass density (kg/m³) to weight density (N/m³)
Weight density in N/m3=2650×9.81=26026.5 N/m3\text{Weight density in N/m}^3 = 2650 \times 9.81 = 26026.5 \, \text{N/m}^3Weight density in N/m3=2650×9.81=26026.5N/m3
Step 2: Convert N/m³ to lb/ft³
Use the conversions:
- 1 N=0.224809 lb1 \, \text{N} = 0.224809 \, \text{lb}1N=0.224809lb
- 1 m3=35.3147 ft31 \, \text{m}^3 = 35.3147 \, \text{ft}^31m3=35.3147ft3
Weight density in lb/ft3=26026.5×0.22480935.3147\text{Weight density in lb/ft}^3 = \frac{26026.5 \times 0.224809}{35.3147}Weight density in lb/ft3=35.314726026.5×0.224809=5849.4635.3147≈165.7 lb/ft3= \frac{5849.46}{35.3147} \approx 165.7 \, \text{lb/ft}^3=35.31475849.46≈165.7lb/ft3
✅ Final Answer:
165.7 lb/ft³
📘 Explanation
Weight density is the weight per unit volume of a substance. While mass density tells us how much mass is packed into a given volume, weight density considers the force of gravity acting on that mass. This is important in construction, geology, and material science when assessing the load materials can impose.
Granite is a dense igneous rock commonly used in building and engineering. In SI units, its mass density is given as 2650 kg/m³. But engineers working in U.S. customary units often need to know the weight density in pounds per cubic foot.
To perform this conversion, we first find the weight density in Newtons per cubic meter by multiplying the mass density by gravitational acceleration, 9.81 m/s². This gives the weight per unit volume in Newtons.
Since the final answer is required in pounds per cubic foot (lb/ft³), we need to convert Newtons to pounds and cubic meters to cubic feet. One Newton equals about 0.224809 pounds, and one cubic meter equals about 35.3147 cubic feet. By applying these conversions, we translate the SI-based value to U.S. customary units.
The calculated result is approximately 165.7 lb/ft³. This value helps professionals estimate the total weight granite might exert over a given area, important for foundations, structural integrity, or when transporting material.
