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NDA Simple Machines

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This page covers NDA Simple Machines with complete concept notes, 7 graded practice MCQs, key points and exam-specific tips. Free to study.

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Concept Notes

Simple Machines— Rules & Concept

1.Core Concept

Read this first — the foundation of the topic
There are six basic simple machines

lever, pulley, inclined plane, wedge, screw, and wheel-and-axle. Each works on the principle of mechanical advantage, which means the output force is greater than the input force

KEY RULES

Mechanical Advantage (MA) = Output Force / Input Force 2

Work is always conserved

Input Work = Output Work (ignoring friction) 3. If MA > 1, the machine multiplies force. If MA < 1, it increases distance/speed. 4. Efficiency = (Useful Output Work / Input Work) × 100%

2.Formula Block

Memorise — at least one formula appears in every paper
Mechanical Advantage = Load / Effort
Work = Force × Distance
Efficiency (%) = (Output Work / Input Work) × 100
Velocity Ratio = Distance moved by effort / Distance moved by load

3.Exam Patterns

What examiners ask — read before attempting PYQs
RRB Group D typically asks

(1) Calculate MA from given load and effort. (2) Identify which simple machine is shown in a diagram. (3) Compare efficiency or work done. (4) Real-world applications (e.g., ramps, scissors, door handles)

SHORTCUT

Always remember: No machine can have efficiency > 100% due to friction. If a question shows MA = 4 and efficiency = 80%, then useful work output is only 80% of what the ideal machine would give.

4.Worked Example

Solve this step-by-step before moving on

A man uses a lever to lift a 600 N load. He applies an effort of 150 N. Find: (a) Mechanical Advantage, (b) Velocity Ratio if effort moves 2 m and load moves 0.4 m, (c) Efficiency. Solution: (a) MA = Load / Effort = 600 / 150 = 4 (b) Velocity Ratio = 2 / 0.4 = 5 (c) Efficiency = (MA / VR) × 100 = (4 / 5) × 100 = 80%

5.Exam Traps

Common mistakes students make — avoid these

Students confuse Mechanical Advantage with Velocity Ratio. MA compares forces; VR compares distances. They're different values!

Also, assuming a machine with high MA has high efficiency—not always true due to friction losses.

Key Points to Remember

  • Simple machine multiplies force (effort) by reducing distance moved or changing force direction.
  • Mechanical Advantage = Load / Effort; value >1 means force is multiplied.
  • Velocity Ratio = Distance moved by effort / Distance moved by load; always independent of friction.
  • Efficiency = (Useful Work Output / Work Input) × 100%; always <100% in real machines.
  • Six types: lever, pulley, inclined plane, wedge, screw, wheel-and-axle.
  • Remember: Work input = Work output (ideal); efficiency accounts for friction losses.

Exam-Specific Tips

  • Mechanical Advantage formula: MA = Load / Effort (dimensionless ratio).
  • Velocity Ratio formula: VR = Distance moved by effort / Distance moved by load (always > MA in real machines).
  • Efficiency formula: η = (MA / VR) × 100%; always expressed as percentage.
  • Class 1 Lever has fulcrum between effort and load; MA can be >1, =1, or <1 depending on position.
  • Class 2 Lever has load between fulcrum and effort; always MA >1 (mechanical advantage guaranteed).
  • Class 3 Lever has effort between fulcrum and load; always MA <1 (speed and range advantage).
  • Ideal Machine (frictionless): MA = VR; Real Machine: MA < VR always due to friction.
  • Inclined Plane MA = Length of slope / Height of slope; reduces effort needed to lift vertically.
Practice MCQs

Simple Machines — Practice Questions

7graded MCQs · easy to hard · full solution & trap analysis

All MCQs →
Practice 1medium

A wedge is used to split a log. The wedge has a length of 20 cm and a thickness of 4 cm at its base. What is the mechanical advantage of this wedge? (Assume the wedge is ideal.)

Practice 2medium

A lever of length 2 m has its fulcrum at 0.5 m from one end. If a load of 300 N is placed at the end nearest the fulcrum, what effort is needed at the other end to balance the lever? (Assume the lever is ideal.)

Practice 3medium

A movable pulley system uses 4 supporting ropes to lift a load. If the load is 800 N, what is the minimum effort required to lift it? (Assume the pulley system is ideal with no friction.)

Practice 4medium

A simple machine has a mechanical advantage of 4. If an effort of 50 N is applied to lift a load, what is the load being lifted? (Assume the machine is ideal with no friction losses.)

Practice 5medium

A movable pulley system is used to lift a load of 1200 N. If the effort applied is 400 N, what is the mechanical advantage of this pulley system?

Practice 6medium

An inclined plane of length 5 m is used to raise a load of 1000 N to a height of 3 m. Assuming no friction, what is the effort required to push the load up the plane?

Practice 7hard

A movable pulley system is used to lift a load of 1200 N. If the effort applied is 400 N and the length of the effort rope pulled is 3 m, what is the mechanical advantage and distance moved by the load respectively?

60-Second Revision — Simple Machines

  • Formula: MA = Load / Effort; VR = Distance by effort / Distance by load; Efficiency = (MA/VR) × 100.
  • Remember: No real machine has efficiency = 100%; friction always reduces useful output work.
  • Trap: High MA doesn't mean high efficiency—check friction losses and compare MA to VR.
  • Class 1 Lever (fulcrum centre) varies MA; Class 2 (load centre) MA always >1; Class 3 (effort centre) MA always <1.
  • Quick Check: If MA = 5 and VR = 6, efficiency = (5/6)×100 ≈ 83%—this is realistic and acceptable.
  • Application Memory: Ramp = inclined plane; Scissors = Class 1 lever; Crane = pulley system; Doorknob = wheel-axle.
  • Formula to remember: Input Work (Effort × Distance) = Output Work (Load × Distance) in ideal case only.
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