Find the torque about each end of 4.0 ft log bar if 3.0 lb force acts vertically upword on it 1.0 ft from the right hand end.

If the force is perpendicular to the bar, then the arms of
the moment are measured along the bar.

Since the bar is of
4.0 ft long, the right hand end arm is 1.0 ft, then the left hand end arm is: 4.0 - 1.0
= 3.0 ft.

The formula of the torque
is:

L = F*arm

 We'll calculate
the torque about the left hand end:

F =
3lb.

left hand end arm = 3.0
ft

Ll = 3 lb.*3.0 ft = 9.0 lb-ft
counterclockwise

 We'll calculate the torque about
the right hand end:

F =
3lb.

right hand end arm = 1.0
ft

Lr = 3 lb.*1.0 ft = 3.0 lb-ft
clockwise

Since the torques produced by the given force are
different in direction and magnitude, the bar will twist through an angle that is
proportional to the torque.