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A tank of oil has a mass of 25 slugs. (a) Determine its weight in pounds and in newtons at the Earth's surface. (b) What would be its mass (in slugs) and its weight (in pounds) if located on the moon's surface where the gravitational at raction is approximately one-sixth that at the Earth's surface?

Short Answer

Expert verified
The weight of the oil tank on Earth is 805 lb or 3580 N. Its weight on the Moon would be 134.25 lb, and its mass, on both the Earth and the Moon, is 25 slugs.

Step by step solution

01

Calculate weight on Earth

First, calculate the weight of the oil tank on Earth. The formula to calculate weight is \( W = m × g \) where \( m \) is the mass and \( g \) is the gravitational constant. On Earth, \( g = 32.2 ft/s² \). So, \( W = 25 slugs × 32.2 ft/s² = 805 lb \).
02

Convert pounds to newtons

To convert pounds to newtons, use the conversion factor \( 1 lb = 4.44822 N \). So, \( 805 lb = 805 × 4.44822 N = 3580 N \). That's the weight of the oil tank on Earth in newtons.
03

Calculate mass on the Moon

The mass of the object doesn't change, irrespective of its location. So, the mass of the oil tank on the Moon remains the same as Earth, which is 25 slugs.
04

Calculate weight on the Moon

The gravitational constant on the Moon is approximately one-sixth of that on Earth, i.e., \( g_{moon} = 32.2 ft/s²/6 = 5.37 ft/s² \). So the weight of the oil tank on the Moon would be \( W_{moon} = m × g_{moon} = 25 slugs × 5.37 ft/s² = 134.25 lb \)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Weight calculation
To calculate weight, you need to understand the relationship between mass and the gravitational force acting on it. The formula for calculating weight is stated as \( W = m \times g \) where:
  • \( W \) represents the weight, which is the force exerted by gravity on the object.
  • \( m \) is the mass of the object.
  • \( g \) is the gravitational constant or acceleration due to gravity.
On Earth's surface, the gravitational constant \( g \) is approximately \( 32.2 \text{ ft/s}^2 \). Thus, by multiplying the mass, which in this case is given as \( 25 \) slugs, by the gravitational constant, you get the weight on Earth.

For example, with a mass of \( 25 \) slugs: \[ W = 25 \times 32.2 = 805 \text{ lb} \]


Knowing how to calculate weight is essential in various fields, including engineering and physics. It enables students to understand and compute the forces acting on objects in real-world scenarios.
Gravitational forces
Gravitation is a natural phenomenon by which all things with mass or energy are brought toward one another. It is expressed by the gravitational force. On Earth, this force provides weight to physical objects and is expressed as \( g = 32.2 \text{ ft/s}^2 \).

Gravitational Influence on the Moon

The Moon has a weaker gravitational pull compared to Earth. Specifically, its gravitational force is about one-sixth of Earth's. This small difference significantly affects how weight is perceived.

On the Moon, the gravitational acceleration \( g_{moon} \) is calculated as:

\[g_{moon} = \frac{32.2}{6} \approx 5.37 \text{ ft/s}^2\]
This decrease in gravitational force results in reduced weight for the same mass when measured on the Moon. Knowing these differences is crucial for calculations in astronomical studies and space missions.
Unit conversion
Unit conversion is vital in fluid mechanics and physics for ensuring equations and measurements are consistent and meaningful. Especially when dealing with weight, converting units between systems is often necessary.

Converting Pounds to Newtons

The conversion between pounds and newtons is important because these units measure weight in different systems. Pounds are part of the British system, while newtons belong to the International System of Units (SI). To convert pounds to newtons:
  • Use the factor \( 1 \text{ lb} = 4.44822 \text{ N} \).
  • Multiply the weight in pounds by this conversion factor to find its equivalent weight in newtons.
For instance, converting \( 805 \) pounds to newtons:\[805 \times 4.44822 = 3580 \text{ N}\]
These conversions help scientists and engineers communicate measurements across different cultures and systems, ensuring precision in their work.
Mass and weight differences
Understanding the distinction between mass and weight is essential in fluid mechanics and physics. Mass is a measure of the amount of matter in an object, remaining constant regardless of location. It is usually measured in slugs in the imperial system. Weight, however, is the force that gravity exerts on an object and can vary based on the gravitational environment.For example, the mass of the oil tank is \( 25 \text{ slugs} \) irrespective of whether it's on Earth or the Moon. However, its weight changes because of the differences in gravitational force:
  • On Earth, using the formula \( W = m \times g \), the weight calculated is \( 805 \text{ lb} \).
  • On the Moon, since \( g \) is roughly one-sixth, the weight becomes \( 134.25 \text{ lb} \).
This distinction illustrates that weight is dependent on the local gravitational field, while mass is a fixed quantity. Understanding this difference is crucial for solving problems in physics and engineering correctly.

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Most popular questions from this chapter

A rigid-walled cubical container is completely filled with water at \(40^{\circ} \mathrm{F}\) and sealed. The water is then heated to \(100^{\circ} \mathrm{F}\) Determine the pressure that develops in the container when the water reaches this higher temperature. Assume that the volume of the container remains constant and the value of the bulk modulus of the water remains constant and equal to 300,000 psi.

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