Bennett Mechanical Structures and Center of Gravity Questions and Answers

Question 1

Four objects are made of the same uniform material. Which object is the most stable and least likely to tip over if placed on a flat, level surface?

Accepted Answer

A short, wide cone resting on its base

Answer

Stability is determined by two main factors: a low center of gravity and a wide base of support. [2, 5, 8] The short, wide cone has the lowest center of gravity and the widest base relative to its height, making it the most stable of the options. [8]

Question 2

A perfect 'L' shape is created by joining two identical, uniform rectangular blocks of wood at their ends. Where is the center of gravity of the combined 'L' shape located?

Accepted Answer

In the empty space inside the 'corner' of the L.

Answer

The center of gravity is the average position of all the mass in the object. For a composite, non-convex shape like an 'L', the balance point is not within the physical material of either individual block but is located in the open space formed by the corner. [22]

Question 3

Which of the following geometric shapes, when constructed with beams of equal length and joined by pins at its vertices, forms the most rigid structural element?

Accepted Answer

A triangle

Answer

A triangle is an inherently rigid shape. [7, 9] Once its side lengths are fixed, its angles cannot change, preventing deformation under stress. Other shapes like squares or rectangles can easily be deformed into parallelograms without changing their side lengths. [3, 9] This is why triangles are fundamental to truss design in bridges and buildings. [7, 14]

Question 4

To ensure maximum stability and prevent rolling over during a sharp turn, where should a single, heavy crate be placed on the flatbed of a truck?

Accepted Answer

As low and as close to the center of the truck bed as possible.

Answer

Placing heavy items low and centered keeps the vehicle's overall center of gravity low and balanced. [1, 19] A low center of gravity increases stability and reduces the likelihood of tipping during turns or on uneven roads. [5, 10, 13, 19]

Question 5

A horizontal cantilever beam is securely fixed into a wall at one end and extends outwards. If a heavy weight is hung from the free end, where will the beam experience the greatest bending stress?

Accepted Answer

At the point where it is fixed to the wall.

Answer

The point where the beam is fixed to the wall must support the entire weight plus the turning force (moment) created by the weight acting at a distance. This results in the maximum bending moment and therefore the greatest stress at the fixed support. [21, 26]

Bennett Mechanical Test Practice Test

Bennett Mechanical Test Practice Test

Bennett Mechanical Structures and Center of Gravity Questions and Answers