Figure 74: Masses on supported beam
Figure 75: Accelerating cyclist
real and …ctitious force F = ma acting through the centre of mass as shown. Taking moments about point of contact of rear wheel with the ground, mgd
Fh = 0:
(435)
Example 18 An accelerating car as shown in …g 76:We will assume rear-wheel drive; that centre of mass is at height h above the ground; distances d1 and d2 from wheels as shown in the diagram. Real forces are: weight mg; friction F = ma at the driven rear wheels contact with the ground (There is also friction between front wheels and the ground acting in the opposite sense causing the front wheels to turn rather than skid.); normal reactions at wheels, N1 and N2 . We have N1 + N2 = mg:
(436)
In the car’s accelerating frame we add a …ctitious force F = ma as shown. In this frame the car is now in equilibrium. Taking moments about point A, mgd1 N2 =
N2 (d1 + d2 )
1 (mgd1 (d1 + d2 )
mah) =
60
Fh = 0; m (gd1 (d1 + d2 )
(437) ah) ;
(438)