Worked Example 04
The Question
The automatic flag raising system on a horizontal flagpole attached to the vertical outside wall of a tall building has become stuck. The management of the building wants to send a person crawling out along the flagpole to fix the problem. Because of your physics knowledge, you have been asked to consult with a group to decide whether or not this is possible. You are all too aware that no one could survive the 80 m fall from the flagpole to the ground. The flagpole is a 60 kg steel I-beam which is very strong and rigid. One side of the flagpole is attached to the wall of the building by a hinge so that it can rotate vertically. 3 m away, the other end of the flagpole is attached to a strong, lightweight cable. The cable goes up from the flagpole at an angle of 30° until it reaches the building where it is bolted to the wall. The mechanic who will climb out on the flagpole weighs 80 kg including equipment. From the specifications of the building construction, both the bolt attaching the cable to the building and the hinge have been tested to hold a force of 2500 N. Your boss has decided that the worse case is when the mechanic is at the far end of the flagpole, 3 m from the building.
The Answer
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n.b. I made a calculator error in the vertical force component, which should be 294 N. Thanks to Jane Lin for pointing this out!