A vessel of 4 m3contains an oil which weighs 30 kN. The specific weight of this oil is _______
- A4.5 kN/m3
- B6.0 kN/m3
- C7.5 kN/m3Correct
- D10 kN/m3
Solution
Concept
Specific weight (weight density) is the weight of a fluid divided by its volume. We divide total weight by total volume to find it.
Formula
γ = W / V
Step-by-step solution
1. Let's write down the given values from the question. 2. Volume of the oil (V) is 4 m³. 3. Weight of the oil (W) is 30 kN. 4. Now, use the formula for specific weight (γ): γ = W / V. 5. Put the values: γ = 30 kN / 4 m³. 6. Divide 30 by 4 to get 7.5. 7. So, the specific weight is 7.5 kN/m³. Answer: (C) 7.5 kN/m3
Explanation
Specific weight is the weight per unit volume. By dividing 30 kN by 4 m³, we get 7.5 kN/m³, which matches option C.
Why the other options are wrong
A: 4.5 kN/m³ is incorrect because 30 divided by 4 is not 4.5. B: 6.0 kN/m³ is incorrect because 30 divided by 4 is not 6.0. D: 10 kN/m³ is incorrect because 30 divided by 4 is not 10.
Shortcut
Just divide the weight by the volume. 30 / 4 = 7.5 easily.
Common mistake
Students sometimes multiply the volume and weight instead of dividing, or confuse specific weight with mass density.
Correct answer: C) 7.5 kN/m3