Question

23. A uniform ladder rests against a vertical wall where there is negligible friction. The bottom of the ladder rests on rough ground where there is friction. The top of the ladder is at a height h above the ground and the foot of the ladder is at a distance 2a from the wall. The diagram shows the forces which act on the ladder. ladder wt Which equation is formed by taking moments? Wa + Fh= 2W a B Fa+ Wa = Fh. C wa + 2w a= Fh D Wa- 2W a = 2Fh (June 2008/P/Q14)

The answer is A from marking scheme. Can i please have a detail explanation how to obtain the answer?

Answer 1

As we know that ladder is in rest so torque about any point should be equal to zero. so,

1)- Torque about highest point of ladder- (Consedering anyclockwise as -ve)

$\tau _{H}$ = 0

Wa +Fh -W(2a) = 0 ...(1)

2)- Torque about lowest point of ladder- (Consedering anyclockwise as -ve)

$\tau _{L}$ = 0

Fh - Wa =0 ...(2)

Now we can see that Eqn(1) is present in Option (A).

Thankyou !!! Have fun

Please Rate High.