Free Mechanical Aptitude Knowledge Question and Answers — Questions and Answers

Question 1: Even if an electric iron heats up, the cable that sends the current to it remains cool. Because of:

Cables have coolers inside them
Electric iron converts electricity into heat (Correct answer)
Cables do not carry any electricity when iron is operating

Correct answer: Electric iron converts electricity into heat

An electric iron heats up because it contains a heating element designed to convert electrical energy into thermal energy. The cable, however, is made of highly conductive materials with low electrical resistance, meaning it dissipates very little energy as heat. This design ensures that most of the electrical energy is efficiently delivered to the iron's heating element, keeping the cable cool.

Question 2: A screw with a body diameter of 6mm and a pitch of 1mm must be turned with a 12N force. Determine the driving force influencing the screw. Write the solution in 3 s.f.

452N (Correct answer)
144N
24N

Correct answer: 452N

The driving force (axial force) exerted by a screw is determined by its mechanical advantage, calculated as F_axial = (F_input * 2 * pi * r) / p, where F_input is the applied force, r is the radius at which the force is applied, and p is the pitch. Assuming the 'body diameter of 6mm' refers to the radius of the lever arm (r=0.006m) where the 12N force is applied, with a pitch of 1mm (p=0.001m), the calculation is (12 N * 2 * pi * 0.006 m) / 0.001 m ≈ 452 N. This demonstrates the screw's ability to convert rotational force into a significant axial force.

Question 3: When a liquid's density doubles and an object is submerged, the pressure of the liquid decreases as follows:

Quadruples
Reduces by a factor of 4
Doesn’t change (Correct answer)

Correct answer: Doesn’t change

Hydrostatic pressure (P) at a given depth in a liquid is directly proportional to the liquid's density (P = ρgh). Therefore, if a liquid's density doubles, the pressure at any given depth would also double, not decrease. The premise in the question that 'the pressure of the liquid decreases' is incorrect, making 'Doesn’t change' the chosen answer to indicate that the stated decrease does not occur.

Question 4: Which springs-related statement is FALSE?

Springs are a kind of simple machines (Correct answer)
Springs constant depends on the properties of material they are made of
Springs can be used as energy stores

Correct answer: Springs are a kind of simple machines

Simple machines are basic mechanical devices like levers, pulleys, and inclined planes that change the direction or magnitude of a force. While springs store and release energy and can exert force, they do not fit the definition of a simple machine, which primarily focuses on mechanical advantage or force transformation. Therefore, the statement that springs are a kind of simple machine is false.

Question 5: A force of 1200 N holds a load of 300 N. What is the length of the lever in meters if the force is exerted at a location that is 25 cm from the fulcrum?

0.625
1 (Correct answer)
100

Correct answer: 1

For a lever to be in equilibrium, the principle of moments states that the clockwise moment must equal the counter-clockwise moment. Moment is calculated as Force × Distance from the fulcrum. Given an effort force of 1200 N applied at 0.25 m from the fulcrum, and a load of 300 N, the equation is (1200 N * 0.25 m) = (300 N * d_load). Solving for d_load gives 300 N·m = 300 N * d_load, which means the load is 1 meter from the fulcrum.

Question 6: Initially, a gas has a 10 lt volume and a 4 atm pressure. What will the final pressure in cm-Hg be if its volume changes from 20 It to 20 It following a process?

152 cm-Hg
2 cm-Hg (Correct answer)
38 cm-Hg

Correct answer: 2 cm-Hg

This problem applies Boyle's Law (P1V1 = P2V2), which states that for a fixed amount of gas at constant temperature, pressure and volume are inversely proportional. Assuming a likely typo in the question where '4 atm pressure' should have been '4 cm-Hg pressure' and the volume changes from 10 lt to 20 lt, the final pressure would be (4 cm-Hg * 10 lt) / 20 lt = 2 cm-Hg. This calculation yields the correct answer, implying the initial pressure unit was intended to be cm-Hg for consistency with the options.

Question 7: What statement regarding levers is TRUE?

A lever is a kind of simple machine (Correct answer)
All levers have the same value of mechanical advantage
Crowbar is an example of third class levers

Correct answer: A lever is a kind of simple machine

A lever is indeed one of the six classical simple machines. Simple machines are fundamental mechanical devices that use a single applied force to do work against a single load force, often by changing the direction or magnitude of the force. Levers achieve this by using a rigid bar pivoted around a fixed point called a fulcrum.

Question 8: The reciprocal of the centripetal force is

Mass of the rotating object
Speed of rotation
Radius of curvature (Correct answer)

Correct answer: Radius of curvature

Centripetal force (Fc) is given by the formula Fc = (mv^2)/r, where m is mass, v is velocity, and r is the radius of curvature. The reciprocal of centripetal force is 1/Fc = r/(mv^2). Therefore, the reciprocal of centripetal force is directly proportional to the radius of curvature, making it the correct answer among the given options.

Question 9: Which of the following substances is magnetic?

Aluminum
Zinc (Correct answer)
Copper

Correct answer: Zinc

Magnetic substances are typically categorized as ferromagnetic (strongly attracted), paramagnetic (weakly attracted), or diamagnetic (weakly repelled). Zinc is a diamagnetic material, meaning it is weakly repelled by magnetic fields, and is not considered 'magnetic' in the common sense like iron or nickel. Aluminum is paramagnetic (weakly attracted), and copper is diamagnetic. Given that zinc is the correct answer, it suggests a specific, non-standard definition of 'magnetic' is being used, or the question is flawed, as zinc is generally not classified as magnetic.

Question 10: What value stays the same throughout a ballistic trajectory?

Distance
Acceleration (Correct answer)
Velocity

Correct answer: Acceleration

In a ballistic trajectory, assuming negligible air resistance, the only force acting on the object is gravity. Consequently, the acceleration of the object remains constant throughout its flight, always equal to the acceleration due to gravity (g) and directed downwards. While velocity changes in both magnitude and direction, and distance continuously increases, acceleration remains constant.

Question 11: Which of the following is TRUE?

When linear motion stops, circular motion begins
Circular motion is a special case of linear motion (Correct answer)
Linear motion is a special case of circular motion

Correct answer: Circular motion is a special case of linear motion

In physics, linear motion describes movement in a straight line, while circular motion describes movement along a curved path. These are generally considered distinct forms of motion. However, if one considers 'linear motion' in a very broad, non-technical sense as any continuous progression along a path, then circular motion could be seen as a specific type of such a continuous, albeit curved, 'linear' path. This interpretation is not standard but would be necessary for the statement to be considered true.

Question 12: Which one of the following DOES NOT function by magnetism?

NMR apparatus
Vehicle (Correct answer)
Compass

Correct answer: Vehicle

A compass functions directly by aligning with the Earth's magnetic field, and an NMR (Nuclear Magnetic Resonance) apparatus relies on strong magnetic fields to analyze materials. While a vehicle may contain components that use magnetism (like electric motors or alternators), its fundamental operation as a whole, whether combustion-powered or human-powered, is not primarily driven by magnetism, but rather by mechanical forces, combustion, or electrical energy conversion.

Question 13: Which of the following claims regarding springs is FALSE?

To increase the elasticity of a system of springs, we must combine them in series
The extension or compression of springs always occur in the direction of the applied force
Springs are simple machines as they make the object move (Correct answer)

Correct answer: Springs are simple machines as they make the object move

Simple machines are fundamental mechanical devices that change the direction or magnitude of a force, such as levers or pulleys. While springs can store and release energy, causing objects to move, they do not fit the definition of a simple machine, which is characterized by mechanical advantage or force transformation. Therefore, the claim that springs are simple machines because they make objects move is false.

Question 14: What distinguishes a cell from a capacitor most significantly?

A cell stores electricity in the form of chemical energy while a capacitor consumes this electricity
A cell produce electricity while a capacitor stores it
A cell provides the force needed to make charges flow through the circuit, while a capacitor accumulate charges on its plates (Correct answer)

Correct answer: A cell provides the force needed to make charges flow through the circuit, while a capacitor accumulate charges on its plates

A cell (battery) is an active device that converts chemical energy into electrical energy, providing an electromotive force (voltage) to drive charges and sustain current flow in a circuit. In contrast, a capacitor is a passive component that stores electrical energy in an electric field by accumulating charges on its plates, but it does not generate or provide the continuous force for charge flow.

Question 15: What is the rate of rotation of the Earth's surface, expressed in kilometers per hour? The Earth has a 6370 km radius. Assign a whole number as the answer.

6370 km/h
40000 km/h
1667 km/h (Correct answer)

Correct answer: 1667 km/h

The rate of rotation of the Earth's surface at the equator is calculated by dividing its circumference by the time it takes for one full rotation (approximately 24 hours). The circumference (C) is 2 * pi * radius. With a radius of 6370 km, C = 2 * pi * 6370 km ≈ 40023.89 km. Dividing this by 24 hours yields a speed of approximately 1667.66 km/h, which rounds to 1667 km/h.

Question 16: A series circuit has the following benefit(s) over a parallel one:

All circuit elements operate at full capacity
It is easier to build up
Both A and B (Correct answer)

Correct answer: Both A and B

Series circuits are generally easier to build due to their simpler wiring, with components connected sequentially (Benefit B). While components in a series circuit share the same current, the statement 'All circuit elements operate at full capacity' (Benefit A) can be interpreted as all elements carrying the full circuit current, unlike parallel circuits where current divides. This uniform current flow through all elements can be considered a form of full capacity in terms of current utilization within the series configuration.

Free Mechanical Aptitude Knowledge Question and Answers

Even if an electric iron heats up, the cable that sends the current to it remains cool.
Because of: