#### Question

A, B and C are the three forces each of magnitude 4 n acting in the plane of the paper as shown in Figure. The point O lies in the same plane.

1) Which force has the least moment about O? Give a reason.

2) which force has the greatest moment about O? Give a reason.

3) Name the forces producing (a) Clockwise (b) anticlockwise moments.

4) what is the resultant torque about the point O?

#### Solution

1) We know that

Moment of Force = Force x Perpendicular distance

Since the perpendicular distance of vector C is least from the point O.

Vector C will have the least moment about O.

2) We know that

Moment of force = Force x Perpendicular distance

Since the perpendicular distance of vector A is greatest from the point O.

Vector A will have the greatest moment about O.

3.a) Vector A and B will produce clockwise moments.

Explanation: if the turning effect on the body is clockwise.

The moment if force is called clockwise moment and it is taken as negative.

3.b) Vector C will produce anticlockwise moment.

Explanation L if the turning effect on the body is anticlockwise.

Moment of force is called anticlockwise moment and it is taken as positive.

4) Resultant torque about point O = sum of torques due to vectors A, B, and C

∴Resultant torque about point O.

`= -(4 xx 0.9) - (4 xx 0.8) + (4 xx 0.6) Nm`

= -3.6 - 3.2 + 2.4

= -4.4 Nm

The negative sign suggests that the resultant torque is in the clockwise direction.