Question

help please...A funnel-shaped lamp with mass 5.75 kg is suspended by two ropes as shown. The horizontal line is 1.25 m long. The oblique line is 1.55 m long. The angle between the oblique line and the roof is 35 °. Determine the forces acting in the ropes. with explanation please.

Answer 1

Fm (lamp) = 56,4075N (F=m.g Newtons law where m = mass lamp and g = gravitational acceleration)
I used moment of force analysis in the construction in statical balance:
moments around line 2 connection (oblique line) gives:
Mp2 clockwise = Mp2 countercl wise = 1,25m.56,4075N = 70,509375Nm = Fr2.1,25.sin 35° (Fl2 is the force in line 2)
This equation we can solve for Fl2.
moments around line 1 connection gives:
Mp1 clockwise = Mp1 counterclkwise = 56,4075N.1,55.cos35 = 71,62Nm = Fl1.1,55.sin35°
This equation we can solve for Fl1.
Fline1 = 80,56N
Fline2 = 98,3435N

You can check the results by drawing a triangle of forces, the three forces should cancel out, so with resultante zero, since the construction is in statical balance.


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Answer 2

The moments of force around a point in a construction in statical balance are netto zero: we can thus state that the moments of force that act clockwise are equal to the ones that act counterclockwise. The moment of force is calculated as the force times the distance to the point where the moment of force acts on, here the points p1 and p2 on the walls.
A force that has a direction not perpendicular on the line connecting it to the p1 or p2 should be split in its components (see http://en.wikipedia.org/wiki/Net_force), so we treat the forces as vectors that can be added to a net force or split into.

Answer 3

in your exercise the forces act in angles, so we calculate the force's composing forces (we actually split one foce into it's composing forces) with the parallelogram rule.

Answer 4

ty for the help but i think the answer should be simpler, nothing of what u said is mentioned in my book