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%
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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
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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.
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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%
COMMON MISTAKE:
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.
Test Simple Machines under exam conditions
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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 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 3medium
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 4medium
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 5medium
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 6medium
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 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.