Problem 7P

assume T = 20°C and vsound = 343 m/s in air.

Calculate the percent error made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) 30°C, and (b) 10°C.

Solution: Step 1: PSI is defined as the one pound-force applied to one square inch of area. Again one pound-force is defined as the gravitational force exerted by one pound of mass. At first we will convert pound-force to Newton. 35.0 pound-force is given by 2 f = 35 lbf = (35 lb) × g = (35)(0.45 kg)g = (15.75 kg)(9.8 m/s ) = 154.35 N