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Machines look easy in ICSE Class 10 physics until a question gives you a block and tackle, a pulley weight and an efficiency, and asks for the effort. The ideas are few: two ratios and one link between them. This post sets out what the syllabus asks, derives the link, and works through pulley problems with numbers you can check.
What does the ICSE syllabus include on machines?
The ICSE 2027 Physics syllabus places machines in Class X, as "force multipliers". It lists the terms effort E, load L, mechanical advantage MA = L/E, velocity ratio VR = dE/dL, input and output work, and efficiency, with the relation between efficiency, MA and VR "derivation included". It states that for all practical machines efficiency is less than 1 and MA is less than VR. It then covers the three classes of lever and three pulley systems: single fixed, single movable, and block and tackle, with MA, VR and efficiency in each case.
What do MA, VR and efficiency mean?
Mechanical advantage tells you how much the machine multiplies your force. OpenStax College Physics defines it as output force over input force and notes that "a machine cannot do more work than the energy put into it". Velocity ratio tells you how far your hand moves compared with the load. Neither has a unit.
Efficiency is useful work out divided by work in:
Output work = L × dL
Input work = E × dE
Efficiency = (L × dL) / (E × dE) = (L/E) × (dL/dE) = MA / VR
So MA = efficiency × VR. If there were no friction and no moving parts to lift, MA would equal VR. In practice some input work always goes into friction or into lifting the pulleys, so MA is smaller.
How do the three pulley systems compare?
Single fixed pulley: VR = 1. Ideally MA = 1, so it gives no force gain. It is used because pulling down is easier than lifting up: it changes the direction of the force.
Single movable pulley: two strands hold up the pulley, so the load rises 1 m when you pull 2 m of rope. VR = 2, and ideally MA = 2.
Block and tackle: VR equals the number of rope segments holding up the movable block. OpenStax puts it the same way: the number of cables pulling upward on the load is approximately the MA, if the pulleys are frictionless.
One detail to watch: if the effort is applied upward on the free end, that strand also supports the movable block and counts. In the ICSE 2027 specimen physics paper, a block and tackle of three pulleys "with the effort in upward direction" has VR 4 in the marking scheme, not 3.
Worked example 1: a single movable pulley with weight
A load of 300 N hangs from a movable pulley of weight 20 N. Ignore friction. Find the effort, MA and efficiency.
The two strands together support the load and the pulley: 2E = 300 + 20 = 320 N, so E = 160 N.
MA = L / E = 300 / 160 = 1.875.
VR = 2, so efficiency = 1.875 / 2 = 0.9375, or 93.75%.
The machine is not 100% efficient even without friction, because some work goes into lifting the pulley.
Worked example 2: block and tackle with friction
A block and tackle has four pulleys, two in each block, with the effort applied downward. The load is 600 N and the lower block weighs 40 N.
Four segments support the lower block, so VR = 4.
Without friction: 4E = 600 + 40 = 640 N, so E = 160 N, MA = 600 / 160 = 3.75 and efficiency = 3.75 / 4 = 93.75%.
Now suppose the effort actually needed is 200 N (a sample number, as if measured in the lab). MA = 600 / 200 = 3 and efficiency = 3 / 4 = 75%.
Check it with energy. Raise the load 1 m; the effort moves 4 m. Input work = 200 × 4 = 800 J. Useful output = 600 × 1 = 600 J. Of the 200 J lost, lifting the 40 N block 1 m takes 40 J, so 160 J went into friction. Efficiency = 600 / 800 = 75%, matching step 3.
Common mistakes and how to avoid them
Mixing up MA and VR. MA is a force ratio (load over effort); VR is a distance ratio (effort distance over load distance).
Counting every strand. Count only segments that hold up the movable block, plus the effort strand if it pulls upward.
Forgetting the pulley weight. Add it to the load when you balance forces, but use only the load in MA.
Answering 100% efficiency for a real machine. The syllabus states that efficiency is less than 1 for all practical machines.
Giving MA a unit. It is a ratio of two forces, so it has none.
A practice routine for machines
Draw each pulley system once from memory and label E, L and the strands that count. Then solve three problems a day for a week, mixing single pulleys, block and tackle and levers so that you have to choose the method yourself. Our guide to the ICSE Class 10 physics paper shows how this unit fits the paper, and students heading to JEE can see how pulley strings set accelerations in pulley constraint relations.
If counting strands still feels abstract, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
Start now: sketch a block and tackle with three pulleys, effort pulling up, and count the strands until you reach 4.
