Engineering Mathematics and Sciences

Problem 1-13| General Principles| Engineering Mechanics: Statics| RC Hibbeler

Convert each of the following to three significant figures: (a) 20 lb·ft to N·m, (b) 450 lb/ft³ to kN/m³, and (c) 15 ft/h to mm/s.

Solution:

a) 20\:lb\cdot ft=\left(20\:lb\cdot ft\right)\left(\frac{4.448\:N}{1\:lb}\right)\left(\frac{0.3048\:m}{1\:ft}\right)=27.1\:N\cdot m

b) 450\:\frac{lb}{ft^3}=\left(\frac{450\:lb}{1\:ft^3}\right)\left(\frac{4.448\:N}{1\:lb}\right)\left(\frac{1\:kN}{1000\:N}\right)\left(\frac{1\:ft^3}{0.3048^3\:m^3}\right)=70.7\:\frac{kN}{m^3}

c) 15\:\frac{ft}{h}=\left(\frac{15\:ft}{1\:h}\right)\left(\frac{304.8\:mm}{1\:ft}\right)\left(\frac{1\:h}{3600\:s}\right)=1.27\:\frac{mm}{s}