FBD Part 1

How many unknowns can be solved in one 2D statics question?

• 1

• 2

• 3

• 4

Answer explanation

In a 2D statics question, you can solve for a maximum of three unknowns as there are three independent equilibrium equations available: the sum of forces in the x-direction, the sum of forces in the y-direction, and the sum of moments about any point in the plane. 

The van has a mass of 1600 kg with its centre of mass at G.  It has two front wheels and four rear wheels.  Which is the correct free body diagram of the van if it is in the equilibrium condition?

• (A)

• (B)

• (C)

• (D)

The mass of 700 kg is suspended from a trolley which moves along the crane rail. Select the correct free body diagram of the crane rail.

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 The aircraft has a mass of 1800 kg with the centre of gravity located at G. During an engine test, a propeller thrust of T = 3 kN is generated and acts through the centre of mass of the aircraft located at G. The brakes are applied to the two front wheels B so that the aircraft remains stationary during the engine test. You should assume that no braking is applied to the single rear wheel A and that the bearing of the rear wheel A can be considered frictionless. Select the correct free body diagram of the aircraft.

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The winch cable on a tow truck is subjected to a force of T=6kN when the cable is directed at θ = 60°. Select the free body diagram of the tow truck to determine the magnitudes of the total brake frictional force F for the rear set of wheels B and the total normal forces at both front wheels A and both rear wheels B for equilibrium. The truck has a total mass of 4 Mg and mass center at G.

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