Question: Five masses in a region where the acceleration due to gravity is 30.5 ft/s² are as follows: m₁ is 500 g of mass; m₂ weighs 800 gf; m₃ weighs 15 poundals; m₄ weighs 3 lb₍f₎; m₅ is 0.10 slug of mass. What is the total mass express (a) in kilograms, (b) in pounds and in slugs. (poundals = lbₘ*ft/s²)
1. **State the problem:** We have five masses with different units and need to find the total mass in kilograms, pounds, and slugs.
2. **Given data:**
- $m_1 = 500$ g
- $m_2 = 800$ gf (gram-force)
- $m_3 = 15$ poundals
- $m_4 = 3$ lb₍f₎ (pounds-force)
- $m_5 = 0.10$ slug
- Acceleration due to gravity $g = 30.5$ ft/s²
3. **Important formulas and conversions:**
- $1$ slug $= 32.174$ lbₘ (pounds mass)
- $1$ lb₍f₎ $= 1$ pound-force $= 1$ lbₘ $\times g_{standard}$ where $g_{standard} = 32.174$ ft/s²
- $1$ poundal $= 1$ lbₘ $\times 1$ ft/s²
- $1$ gf $= 1$ gram-force $= 1$ g $\times 9.80665$ m/s² (standard gravity)
- $1$ lbₘ $= 0.45359237$ kg
- $1$ slug $= 14.5939$ kg
- $1$ g $= 0.001$ kg
4. **Convert all masses to a common unit, starting with slugs:**
- $m_1 = 500$ g $= 500 \times 0.001 = 0.5$ kg
Convert kg to slugs:
$$m_1 = \frac{0.5}{14.5939} = 0.03426 \text{ slugs}$$
- $m_2 = 800$ gf
Since $1$ gf $= 1$ g $\times 9.80665$ m/s², but gravity here is $30.5$ ft/s², convert gf to lb₍f₎ first:
Convert $800$ gf to Newtons:
$$800 \times 9.80665 \times 10^{-3} = 7.84532 \text{ N}$$
Convert Newtons to pound-force:
$$1 \text{ lbf} = 4.44822 \text{ N} \Rightarrow 7.84532 / 4.44822 = 1.763 \text{ lbf}$$
Convert lbf to slugs:
$$m_2 = \frac{1.763}{30.5} = 0.05782 \text{ slugs}$$
- $m_3 = 15$ poundals
Since $1$ poundal $= 1$ lbₘ $\times 1$ ft/s², mass in lbₘ:
$$m_3 = \frac{15}{30.5} = 0.4918 \text{ lb}_m$$
Convert lbₘ to slugs:
$$m_3 = \frac{0.4918}{32.174} = 0.01528 \text{ slugs}$$
- $m_4 = 3$ lb₍f₎
Convert lb₍f₎ to lbₘ:
$$m_4 = \frac{3}{30.5} = 0.09836 \text{ lb}_m$$
Convert lbₘ to slugs:
$$m_4 = \frac{0.09836}{32.174} = 0.00306 \text{ slugs}$$
- $m_5 = 0.10$ slug (already in slugs)
5. **Sum all masses in slugs:**
$$m_{total} = 0.03426 + 0.05782 + 0.01528 + 0.00306 + 0.10 = 0.21042 \text{ slugs}$$
6. **Convert total mass to kilograms:**
$$m_{total,kg} = 0.21042 \times 14.5939 = 3.071 \text{ kg}$$
7. **Convert total mass to pounds (lbₘ):**
$$m_{total,lb} = 0.21042 \times 32.174 = 6.766 \text{ lb}_m$$
**Final answers:**
- (a) Total mass in kilograms: $3.071$ kg
- (b) Total mass in pounds: $6.766$ lbₘ
- Total mass in slugs: $0.21042$ slugs