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 250 foot fall from the flagpole to the ground. The flagpole is a 120 lb 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. Nine feet 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 150 lbs. 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 500 lbs. Your boss has decided that the worst case is when the mechanic is at the far end of the flagpole, nine feet from the building.

(a) Should you allow the mechanic to climb out to the end of the pole to make the repairs? Provide a quantitative argument for your answer.

(b) Assume the cable holding up the I-beam is made of steel and has a width of 4 mm. In this worst-case scenario, by how much is the cable stretched?

Answer 1

it is safe

We can allow mechanic to climb to make repairs.