Q. Assertion The bridges are declared unsafe after a long use.
ReasonThe bridges lose their elastic strength with time.

 1513  215 Mechanical Properties of Solids Report Error

Solution:

A bridge during its use undergoes alternating strains for a large number of times each day, depending upon the movement of vehicles on it. When a bridge is used for long time, it losses its elastic strength due to which the amount of strain in the bridge for a given stress will become large and ultimately, the bridge may collapse. This may not happens if the bridges are declared unsafe after long use.