Mass of a uniform rod of length 10 m is 10 kg . The rod is placed over knife edges A and B. One end of the rod is resting on the knife edge A and the other end is 2 m outside the knife edge B. A 30-kg weight is now suspended 2 m away from the end A. Find the magnitude of the normal forces on the knife edges.

Explanation

Let `R_(1)` and `R_(2)` be the normal forces at knife edges A and B respectively Fig. The weight of the of the rod, `10 kg xx9.8 "m.s"^(-2)` =99 N, is acting at O, the mid-point of the rod.
From the conditions of equilibrium,
`R_(1) +R_(2)=(30+10)xx9.8=392 N`
Taking moments about the point A,
`R_(2)xxAB = 30xx9.8 xxAD+10xx9.8xxAO`
or, `" " R_(2) xx8 = 294 xx2+98xx5`
`:. R_(2)=134.75 `N
`:. R_(1) = 392 -134.75 = 257.25 `N.