Core ConceptRead 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%
Formula BlockMemorise — 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
Exam PatternsWhat 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.
Worked ExampleSolve 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%
Exam TrapsCommon 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
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.