Fig 1.35 shows two forces each of magnitude 10 N acting at the points

1.	Fig 1.35 shows two forces each of magnitude 10 N acting at the points A and B at a separation of 50 cm, in opposite directions. Calculate the resultant moment of the two forces about the point (i) A, (ii) B and (iii) O, situated exactly at the middle of the two forces.
Answer» (i) Perpendicular distance of point A from the force F = 10 N at B is 0.5m, while it is zero from the force F = 10 N at A Hence, moment of force about A is = 10 N × 0.5m = 5 Nm(clockwise) (ii) Perpendicular distance of point B from the force F = 10 N at A is 0.5m, while it is zero from the force F = 10 N at B Hence, moment of force about B is = 10 N × 0.5m = 5Nm (clockwise) (iii) Perpendicular distance of point O from either of the forces F = 10N is 0.25 m Moment of force F (=10N) at A about O = 10N × 0.25m = 2.5 Nm(clockwise) And moment of force F (=10N) at B about O = 10N × 0.25m=2.5 Nm(clockwise) Hence, total moment of the two forces about O = 2.5 + 2.5 = 5 Nm (clockwise)

Fig 1.35 shows two forces each of magnitude 10 N acting at the points A and B at a separation of 50 cm, in opposite directions. Calculate the resultant moment of the two forces about the point (i) A, (ii) B and (iii) O, situated exactly at the middle of the two forces.

Answer»

(i) Perpendicular distance of point A from the force F = 10 N at B is 0.5m, while it is zero from the force F = 10 N at A

Hence, moment of force about A is

= 10 N × 0.5m = 5 Nm(clockwise)

(ii) Perpendicular distance of point B from the force F = 10 N at A is 0.5m, while it is zero from the force F = 10 N at B

Hence, moment of force about B is

= 10 N × 0.5m = 5Nm (clockwise)

(iii) Perpendicular distance of point O from either of the forces F = 10N is 0.25 m Moment of force F (=10N) at A about O = 10N × 0.25m

= 2.5 Nm(clockwise)

And moment of force F (=10N) at B about O

= 10N × 0.25m=2.5 Nm(clockwise)

Hence, total moment of the two forces about O

= 2.5 + 2.5 = 5 Nm (clockwise)