The fracture strength of glass may be increased by etching away a thin surface layer. it is believed that the etching may alter the surface crack geometry (i. e. reduce crack length and increase tip radius). calculate the ratio of the etched and original crack tip radii if the fracture strength is increased by a factor of 5 when 16.0% of the crack length is removed.

Afoot bridge is made as a simple deck, 4 m long, with a cross section 2 m (wide) and 20 cm thick, and made of wood. the deck is supported at the two ends. the maximum load allowable on the bridge is 10 tons, provided it is uniformly distributed on the deck. to sense this load, a strain gauge is placed at the center of the bridge and its resistance is monitored. if the sensor has a nominal resistance of 350 s2 and a gauge factor of 3.6, what is the reading of the strain gauge at maximum load? the modulus of elasticity for the wood used in the construction is 10 gpa.