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.

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giorgiana1976 | College Teacher | (Level 3) Valedictorian

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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.

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