Evaluate force by replacing equivalent force:

In designing lifting hook, the forces acting on horizontal section through B can be determined by replacing F by equivalent force at point B and a couple. If couple is 3000 N-mm, determine force F for the figure given below.

.: Force 'F' is replaced at B, by a single force 'F' and single couple of magnitude 3000 N-mm.

Now apply the two equal and opposite force that is 'F' at point B. as shown in the figure. Now force 'F' which is act at E and upward force which is act at B makes a couple of magnitude = Force × distance

= F × 40

But  40F = 3000 i.e.

F = 75 N                                                                                  ........ANS