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A car bonnet, represented by QP, of mass 12 kg is pivoted at P. Its weight acts at G where QG = GP = 1.0 m.

A car bonnet, represented by QP, of mass 12 kg is pivoted at P. Its weight acts at-example-1

1 Answer

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The first step is to complete the diagram as shown below

From the information given,

mass of bonnet = 12kg

Weight = mass x acceleration due to gravity

Thus,

Weight of bonnet = 12 x 9.8 = 117.6 N

Thus, the force acting downwards is 117.6 N

Recall, moment = force x distance from pivot perpendicular to the line of action of the force

The distance from pivot perpendicular to the line of action of the force is PB. We would find PB by applying the cosine trigonometric ratio which is expressed as

Cosθ = adjacent side/hypotenuse

Considering triangle GBP,

hypotenuse = 1

adjacent side = BP

Cos30 = BP/1

BP = 1Cos30 = 0.866

Thus,

Moment = 117.6 x 0.866 = 101.845 Nm

The unknown force, F is perpendicular to the pivot and it is 2m from the pivot. The moment created by this force is 2 * F = 2F

Since the bonnet is in equilibrium(Since the mass acts at the center), it means that

2F = 101.845

F = 101.845/2

F = 51 N

A car bonnet, represented by QP, of mass 12 kg is pivoted at P. Its weight acts at-example-1
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