Introduction to Mechanical Reasoning Tests
Mechanical reasoning tests measure your knowledge of straightforward mechanical
and physical concepts. They do not measure your underlying mechanical aptitude in
the same way that abstract reasoning questions measure your underlying intellectual
ability. For example, you could sit an abstract reasoning test without having seen one
before and still get a reasonable score. The same is not true of mechanical reasoning
where your score will depend significantly on your knowledge of:
• Levers
• Pulleys
• Gears
• Springs
• Simple Electrical Circuits
• Tools
• Shop Arithmetic
You may have come across: levers, pulleys, gears, springs and simple circuits in
elementary science and the questions on these topics are fairly straightforward. If
elementary science classes seem like a long time ago then you may need to refresh
your memory before attempting these questions.
Overview of Mechanical Reasoning Tests
In this Article I will only focus on these topic :-
•Levers
• Pulleys
• Gears
• Springs
• Gravity
• Electricity
Levers
A lever consists of a bar which pivots at a fixed point known as the fulcrum. In the
example shown the fulcrum is at the center of the lever. This lever provides no
mechanical advantage and the force needed to lift the weight is equal to the weight
itself.
However, if you want to lift a weight that is heavier than the force applied you can
move the fulcrum closer to the weight to be lifted. This affects the force required in
the following way:
w x d1 = f x d2
Where:
W = weight d1 = distance from fulcrum to weight
f = force needed d2 = distance from fulcrum to point where force is applied.
In this example the fulcrum has been moved towards the weight so that the weight is 1
meter from the fulcrum. This means that the force can now be applied 2 meters from
the fulcrum.
If you needed to calculate the force needed to lift the weight then you can rearrange
the formula.
w x d1 = f x d2 can be rearranged to f = (w x d1)/d2
f = (10 x 1)/2 (10/2 is the same as 5/1, the force required is 5 Kg)
Example Questions
1.How much force is required to lift the weight?
A) 40lbs B) 50lbs C) 60lbs D)70lbs
Answer
C – 60lbs is needed to lift the weight. It can be calculated like this:
f = (w x d1)/d2
f = (80 x 9)/12
f = (720)/12
f = 60 lbs
In practice, levers are used to reduce the force needed to move an object, in other
words to make the task easier. However, in mechanical aptitude questions it is
possible that you will see questions where the fulcrum has been placed closer to the
force than the weight. This will mean that a force greater than the weight will be
required to lift it
You may see more complex questions involving levers, for example, there may be
more than one weight. In this case you need to work out the force required to lift each
weight independently and then add them together to get the total force required.
2.How much force is required to lift the weights?
A) 25lbs B) 35lbs C) 40lbs D)45lbs
Answer.B – 35lbs is needed to lift the weight. It can be calculated like this:
f = (w1 x d1) + (w1a x d1a)/d2
f = (20 x 10) + (30 x 5)/10
f = (200 + 150)/10
f = 35 lbs
Pulleys
The pulleys used in this type of question consist of a grooved wheel and a block
which holds it. A rope runs in the groove around the wheel and one end will be
attached to either: a weight, a fixed object like the ceiling or to another pulley. For the
purposes of these questions you can ignore the effect of friction.
Single Pulley
Which weight requires the least force to move?
Answer
3. B – Weight B requires a force equal to 5 Kg whereas A requires a force equal to 10
Kg.
Single pulley questions are relatively straightforward. If the pulley is fixed, then the
force required is equal to the weight. If the pulley moves with the weight then the
force is equal to half of the weight. Another way of thinking about this is to divide the
weight by the number of sections of rope supporting it to obtain the force needed to
lift it. In A there is only one section of rope supporting the weight, so 10/1 = 10 Kg
required to lift the weight. In B there are two sections of rope supporting the weight,
so 10/2 = 5 Kg required to lift it.
Double Pulleys
There are two possible ways that two pulleys can be used. Either one pulley can be
attached to the weight or neither of them can be.
4. Which weight requires the least force to move?
Answer
A – Weight A requires a force equal to 5 Kg whereas weight B requires a force
equal to 10 Kg. Remember to divide the weight by the number of sections of rope
supporting it to get the force needed to lift the weight
Using More Than Two Pulleys
5. How much force is required to move the weight?
A) 100 Kg B) 150 Kg C) 50 Kg D) 60 Kg
Answer
5. C – The weight is 300 Kg and there are 6 sections of rope supporting it. Divide 300
by 6 to get 50 Kg. In all cases, just divide the weight by the number of sections of
rope supporting it to get the force needed to lift the weight.
Gears
A gear is a toothed wheel or cylinder that meshes with another toothed component to
transmit motion or to change speed or direction. Gears are attached to a rotating shaft
turned by an external force, which is not usually illustrated in these types of question.
Two gears may be connected by touching each other directly or by means of a chain
or belt. If gears are connected by a chain or belt then they move in the same direction.
If the gears are touching (meshed) then adjacent gears move in opposite directions. In
this example the first and third gear will turn in the same direction. When there are an
odd number of meshed gears then the last gear will always turn in the same direction
as the first one.
Meshed gears with an equal number of teeth will turn at the same speed. If they have
an unequal number of teeth then the gear with the fewest teeth will turn faster. To
work out how fast one is turning with respect to the other you need to count the teeth.
Springs
A spring is piece of wire or metal that can be extended or compressed by an external
force but which then returns to its original length when that force is no longer applied.
There are many different types of spring including, spiral coil, leaf springs and torsion
springs. Springs are used in many applications including clocks, vehicle suspensions
etc. In the type of questions that you will be asked in mechanical aptitude tests, you
can assume that springs behave in a linear way. That is, doubling the force applied
will stretch or compress the spring twice as much.
Springs in Series & Parallel
If more than one spring is used then they can be arranged in one of two ways, either in
series or in parallel.
When springs are arranged in series, each spring is subjected to the force applied.
When the springs are arranged in parallel the force is divided equally between the
springs
Example Question
6. A force of 5 Kg compresses the springs in series by 10cm.What will be the total
distance that the springs in parallel are compressed?
A) 10 cms B) 2.5 cms C) 5 cms D) 7.5 cms
Answer
6. C – The total force will be divided equally between the 2 springs in parallel. Since
the force is divided in half, the distance moved will also be halved. The springs in
series were compressed by10 cms, therefore the springs in parallel will be compressed
by 5 cms
Electricity
Questions on electricity usually take the form of simple circuit diagrams.
These diagrams are usually restricted to showing the power source, switches, loads
(typically bulbs), and the path of the wiring. To answer these questions you need a
basic understanding of how electricity flows around a circuit.
