Problem 1-12| General Principles| Engineering Mechanics: Statics| RC Hibbeler

Convert each of the following and express the answer using an appropriate prefix: (a) 175 lb/ft³ to kN/m³, (b) 6 ft/h to mm/s, and (c) 835 lb·ft to kN·m.

Solution:

a) $175\:lb/ft^3=\left(\frac{175\:lb}{ft^3}\right)\left(\frac{1\:ft}{0.3048\:m}\right)^3\left(\frac{4.448\:N}{1\:lb}\right)=27.5\left(10\right)^3\:\frac{N}{m^3}=27.5\:kN/m^3$

b) $6\:ft/h=\left(\frac{6\:ft}{1\:h}\right)\left(\frac{0.3048\:m}{1\:ft}\right)\left(\frac{1\:h}{3600\:s}\right)=0.508\left(10^{-3}\right)\:\frac{m}{s}=0.508\:mm/s$

c) $835\:lb\cdot ft=835\:lb\cdot ft\:\left(\frac{4.448\:N}{1\:lb}\right)\left(\frac{0.3048\:m}{1\:ft}\right)=1.13\left(10^3\right)N\cdot m=1.13kN\cdot m$