0
0

Work, Energy and Power Concepts

Introduction

The concepts of work, energy, and power form the foundation of mechanics in physics and are frequently asked in exams like SSC CGL, RRB NTPC, and IBPS PO. Understanding these concepts helps in solving problems related to force, motion, and energy transformations.

Pattern: Work, Energy and Power Concepts

Pattern

This pattern tests the understanding of the definitions, formulas, and units related to work done by a force, different forms of energy, and power as the rate of doing work.

Key Concept:

Work done (W) = Force (F) × Displacement (d) × cos θ; Energy is the capacity to do work; Power (P) = Work done / Time taken

Important Points:

  • Work = Product of force and displacement in the direction of force; measured in Joules (J)
  • Energy = Ability to do work; common forms include kinetic and potential energy
  • Power = Rate of doing work; SI unit is Watt (W), where 1 Watt = 1 Joule/second

Related Topics:

  • Newton's Laws of Motion
  • Conservation of Energy
  • Simple Machines and Mechanical Advantage

Step-by-Step Example

Question

SSC CGL 2022: A force of 10 N acts on an object and moves it through a distance of 5 m in the direction of the force. What is the work done by the force?

Options:

  • A. 2 Joules
  • B. 50 Joules
  • C. 15 Joules
  • D. 5 Joules

Solution

  1. Step 1: Identify given values

    Force (F) = 10 N, Displacement (d) = 5 m, Angle θ = 0° (force and displacement in same direction)

  2. Step 2: Apply work formula

    Work done, W = F × d × cos θ = 10 × 5 × cos 0° = 10 × 5 × 1 = 50 Joules

  3. Step 3: Calculate final value

    Work done = 50 Joules

  4. Final Answer:

    50 Joules → Option B

  5. Quick Check:

    Work done = Force × Displacement × cos θ = 50 Joules ✅

Quick Variations

This pattern may appear as calculation of kinetic or potential energy, power output of machines, or conceptual questions on units and definitions of work, energy, and power.

Trick to Always Use

  • Remember: Work is zero if displacement is zero or force is perpendicular to displacement (cos 90° = 0)
  • Mnemonic for energy forms: "Kinetic is motion, Potential is position"

Summary

Summary

  • Work = Force × Displacement × cos θ, unit is Joule (J)
  • Energy is the capacity to do work; kinetic and potential are common types
  • Power = Work done / Time, unit is Watt (W)

Remember:
“Work done depends on force, displacement, and angle between them”

Practice

(1/5)
1. SSC CGL 2023: What is the SI unit of power?
easy
A. Pascal
B. Joule
C. Newton
D. Watt

Solution

  1. Step 1: Identify the concept

    The question asks about the SI unit of power, which is the rate of doing work.

  2. Step 2: Apply the concept

    Power is defined as work done per unit time and its SI unit is Watt (W), where 1 Watt = 1 Joule/second.

  3. Final Answer:

    Watt → Option D

  4. Quick Check:

    Power unit = Watt ✅
Hint: Remember: Power = Work/Time, unit is Watt.
Common Mistakes: Confusing Joule (unit of work) with Watt (unit of power).
2. RRB NTPC 2023: When does the work done by a force become zero?
easy
A. When force is maximum
B. When force and displacement are in the same direction
C. When displacement is zero
D. When displacement is maximum

Solution

  1. Step 1: Understand the concept

    Work done depends on force, displacement, and the angle between them.

  2. Step 2: Analyze conditions for zero work

    If displacement is zero, no matter how much force is applied, work done = Force × 0 = 0.

  3. Final Answer:

    When displacement is zero → Option C

  4. Quick Check:

    Work done = 0 when displacement = 0 ✅
Hint: Work = Force × Displacement × cos θ; zero displacement means zero work.
Common Mistakes: Assuming work is zero when force is maximum or displacement is maximum.
3. SSC CHSL 2022: Which of the following is a form of potential energy?
easy
A. Energy stored due to position
B. Energy of motion
C. Kinetic energy
D. Heat energy

Solution

  1. Step 1: Identify the concept

    Potential energy is energy stored due to the position or configuration of an object.

  2. Step 2: Apply the concept

    Energy stored due to position is potential energy, unlike kinetic energy which is energy of motion.

  3. Final Answer:

    Energy stored due to position → Option A

  4. Quick Check:

    Potential energy = Energy stored due to position ✅
Hint: Mnemonic: Potential = Position, Kinetic = Motion.
Common Mistakes: Confusing kinetic energy with potential energy.
4. RRB Group D 2023: A force of 20 N moves an object 3 m at an angle of 60° to the direction of force. What is the work done by the force?
medium
A. 30 Joules
B. 60 Joules
C. 10 Joules
D. 0 Joules

Solution

  1. Step 1: Understand the formula

    Work done, W = Force × Displacement × cos θ.

  2. Step 2: Calculate work done

    Given Force = 20 N, Displacement = 3 m, θ = 60°.
    cos 60° = 0.5.
    W = 20 × 3 × 0.5 = 30 Joules.

  3. Final Answer:

    30 Joules → Option A

  4. Quick Check:

    Work done = F × d × cos θ = 30 Joules ✅
Hint: Use cos 60° = 0.5 to simplify calculations.
Common Mistakes: Ignoring the angle or using sin instead of cos.
5. SSC MTS 2023: If a machine does 500 Joules of work in 10 seconds, what is its power output?
medium
A. 5000 Watts
B. 50 Watts
C. 5 Watts
D. 0.05 Watts

Solution

  1. Step 1: Recall power formula

    Power = Work done / Time taken.

  2. Step 2: Calculate power

    Work done = 500 Joules, Time = 10 seconds.
    Power = 500 / 10 = 50 Watts.

  3. Final Answer:

    50 Watts → Option B

  4. Quick Check:

    Power = Work / Time = 50 Watts ✅
Hint: Divide work by time to get power in Watts.
Common Mistakes: Multiplying work and time instead of dividing.

Mock Test

Ready for a challenge?

Take a 10-minute AI-powered test with 10 questions (Easy-Medium-Hard mix) and get instant SWOT analysis of your performance!

10 Questions
5 Minutes