-3

A) A traffic light with a mass of 140 kg is hung up as shown in the figure above. Calculate the forces in cables AB and AC

I got answer 1.33 kN, which is the correct solution. I used trigonometry and and decomposed the forces from the ropes. Excercise a

B) A parade will pass the traffic light, and the local municipal engineer proposes to install one extra cable DE with a length of 20 m to have a greater free height below point A. The cable section BD is now 10.05 m long. Is this possible when the maximum tension the cables can withstand is 6 kN?

I have done the a part, but I am going to include it here. The answer of a is 1.33 kN We have given that the weight of the traffic light is 140 kg. I don't understand how am I supposed to calculate the forces in b). I have gotten two new robes so there needs to be more forces in this system. Also the new robe is making an angle. The answer is supposed to be above 6 kN, but I am not getting it. Could someone give a tip please?

Exercise B

Ottavio
  • 2,287
Ice_cremy
  • 1
  • 1
    please try to include A, and refer to: https://math.meta.stackexchange.com/questions/9959/how-to-ask-a-good-question – person Jan 13 '21 at 18:21
  • Yes I am going to do it – Ice_cremy Jan 13 '21 at 18:22
  • Hi, I need help from you to demonstrate what work you've done, and how you arrived at the answer of 133 kN for the a part? What part is that? Please give a detailed discussion about your confusion, and why you feel stuck. – amWhy Jan 13 '21 at 18:23
  • I have edited the post. Sorry for the confusion. It is the first time I have posted here. – Ice_cremy Jan 13 '21 at 18:29

1 Answers1

0

Comment

A sketch is necessary to be drawn. The following schematic sketch is given to help get started in posing the question as I understood it. It is not fully correct. It may be later deleted.

enter image description here

To push up the traffic light the engineer suspends two smaller lights as shown at 20 m distance apart without extra cable length but with same total weight. (It is 16.012 m below top line of posts if calculated). The cable is position is elevated to black from red at start.

When a 20 meters rope is added and points B,C are brought nearer to the posts, lights are pushed further up as in green position.

The calculation of forces is done by drawing triangle of static forces.

Narasimham
  • 40,495