## woleraymond 3 years ago a 150kg ladder leans against a smooth wall,making an angle 30 degrees with the floor.The center of gravity of the ladder is one third the way up from the bottom. How large a horizontal force must the floor provide if the ladder is not to slip?

1. ujjwal

Do you have a diagram? the floor provides horizontal force to what? the ladder or wall.. I guess you are talking about ladder.. But are you sure it is the center of gravity of wall whose position is given? I guess it should be of ladder..

2. woleraymond

yes the question modified....

3. woleraymond

guys i need help @experimentX @Vincent-Lyon.Fr

4. Vincent-Lyon.Fr

Are you sure the 30° angle is with the floor and not with the wall?

5. Vincent-Lyon.Fr

Since the ladder is in equilibrium, net torque about any point must be zero. Chose point A where ladder is touching the floor.|dw:1337890332208:dw| It will allow you to find the value of $$N_B$$. Then write that net force is also zero. Finding horizontal component of $$\vec R_A$$ is obvious.

6. woleraymond

the 30degrees is with the floor

7. Vincent-Lyon.Fr

Ok, now, have you tried applying the method I described earlier?

8. woleraymond

no idea @Vincent-Lyon.Fr

9. Vincent-Lyon.Fr

Do you know how to express the moment (torque) of a force about a certain point?

10. woleraymond

yep i do but get confused with the center of gravity constraint

11. Vincent-Lyon.Fr

What do you mean "constraint"?

12. woleraymond

the fact that the center of gravity of the ladder is one third the way up from the bottom.

13. Vincent-Lyon.Fr

Well, as you know where it is, you know its distance from A is l/3. That enables you to work out moment of weight about point A.

14. woleraymond

pls i need help its not clear..since the lenght of AB is not given..aw do we work out moment about point A

15. woleraymond

|dw:1340887287738:dw| 30cos50 X 150 = R X bc

16. woleraymond

@Vincent-Lyon.Fr u dig me?

17. theyatin

according to me no matter where the center of gravity lies. horizontal force applied must be 150cos30' .

18. Vincent-Lyon.Fr