Den Hartog’s Mechanics

A web-based solutions manual for statics and dynamics

Problem 29

When the truck is on the verge of tipping, the front wheels will start to lift off the ground and the forces at the front wheels will be zero. Using this fact, we draw the free-body-diagram for part a) like this:

The equilibrium equation for moments about point B is

\sum M_B = 4\,L_1 - 7000\,\cdot\,8 = 0

and the solution is L_1 = 14,000\,\rm{lbs}.

The FBD for part b) is

and the moment equilibrium equation is

\sum M_B = 4\,L_2\,\cos 30^\circ + 10\,L_2\, \sin 30^\circ - 7000\,\cdot\,8 = 0

and the solution is L_2 = 6,616\,\rm{lbs}. Again, I attribute the weird roundoff error in Den Hartog’s answer to difficulties in getting the third significant digit on a slide rule.

Problem 30Problem 28

Last modified: January 22, 2009 at 8:32 PM.