You Have Been Asked to Help Suspend a Road-Sign Over

Multiple Choice

You have been asked to help suspend a road-sign over a narrow Hobart street. The sign has a mass of 100 kg and will need to be suspended from the end of a 5-m long steel beam which will be attached at the other end to a building. If the beam has a square cross-section, how thick will it need to be to carry the weight without sagging by more than a centimetre? Young's modulus for steel is 2.0x1011 N m-2.

A) 20 cm.
B) 15 cm.
C) 12.5 cm.
D) 10 cm.
E) 7.5 cm.