Chapter 1 - Problems: Developing Engineering Skills - Page 30: 1.15

Here, m=4.5 lb a=3g, taking the summation of all forces along the z direction (upward), we get F - $F_{grav}$ = ma so , F = ma + $F_{grav}$ putting values of the given quantities, F = ma + mg F = 3mg + mg F = 4mg applying conversion into lbf, F= (4.5 lb)( 4$\times$ 32.2 ft/$sec^{2}$)( lbf/ (32.2 lb.ft/$sec^{2}$)) = 18 lbf

Here, m=4.5 lb a=3g, taking the summation of all forces along the z direction (upward), we get F - $F_{grav}$ = ma so , F = ma + $F_{grav}$ putting values of the given quantities, F = ma + mg F = 3mg + mg F = 4mg applying conversion into lbf, F= (4.5 lb)( 4$\times$ 32.2 ft/$sec^{2}$)( lbf/ (32.2 lb.ft/$sec^{2}$)) = 18 lbf