A block of mass 20 kg is hoisted to a height of 5 m above the ... | General Science MCQ | Examoogle

General SciencePhysics: Work, Energy and Power

A block of mass 20 kg is hoisted to a height of 5 m above the ground. Calculate the gravitational potential energy gained by the block. (Take g = 9.8 m/s²)

980 J

100 J

490 J

500 J

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral SciencePhysics: Work, Energy and Power

Option A

980 J

Quick Summary:

Gravitational potential energy is the energy possessed by an object due to its position relative to a reference level, such as the Earth's surface. By substituting the given values of mass ( $m = 20\, \text{kg}$ ), acceleration due to gravity ( $g = 9.8\, \text{m/s}^2$ ), and height ( $h = 5\, \text{m}$ ) into the standard formula, we calculate the energy gained to be $980\, \text{J}$ .

🔬SCScience SolutionConcept & Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of lifting a heavy water bucket to the top shelf; the more you lift it, the more 'potential' it has to fall back down and perform work if released, which is the physical manifestation of stored energy.

🧠 Memory Mnemonic / Shortcut Aid

M-G-H: MyGreat Height (Mass $\times$ Gravity $\times$ Height).

🔢 Key Formulas

$PE = m \times g \times h$ — Gravitational potential energy formula where $m$ is mass, $g$ is acceleration due to gravity, and $h$ is height.

⚙️ Working Principle

The work done against the force of gravity to move an object to a certain height is stored as potential energy. Since the gravitational force acting on the block is $F = m \times g$ , the energy required to raise it through a vertical displacement $h$ is equivalent to the work done, defined as $W = F \times h$ . Thus, potential energy is a function of the object's mass, the gravitational constant, and its vertical elevation.

📌 Key Points

▸
Potential energy is a scalar quantity measured in Joules (J).
▸
It is directly proportional to mass and height; doubling either will double the potential energy.
▸
The value of $g$ is taken as $9.8\, \text{m/s}^2$ on Earth's surface as a standard approximation.

✅ Advantages

▸
Allows for easy calculation of work capacity in mechanical systems.

❌ Disadvantages / Limitations

▸
Does not account for non-conservative forces like air resistance during the hoisting process.

🛠️ Applications / Uses

▸
Hydroelectric power generation using water stored at heights.
▸
Energy storage in mechanical clock pendulums or weights.

📄 Additional Information

▸
SI unit of energy is the Joule, where $1\, \text{J} = 1\, \text{kg} \cdot \text{m}^2/\text{s}^2$ .
▸
Option B ( $100\, \text{J}$ ) results from failing to multiply by gravity. Option C ( $490\, \text{J}$ ) is derived if one incorrectly uses $g = 4.9$ or forgets to double the product.
▸
Option D ( $500\, \text{J}$ ) is obtained by simply multiplying mass by height ( $20 \times 5$ ).

📊 Diagram / Illustration

✅

A is correct — The gravitational potential energy gained is calculated using the formula $PE = mgh$ , which equals $20 \times 9.8 \times 5 = 980\, \text{J}$ .

Core Concepts Used

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Gravitational Potential Energy Work-Energy Theorem Mechanical Energy

💡 EXAM TIP

In competitive exams, always check if the question implies 'g = 10 m/s²' or 'g = 9.8 m/s²'. Using 10 instead of 9.8 is a common trap that changes the result significantly.

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