Physics questions ( I posted all my work)

A uniform rod AB is 1.2 m long and weighs 16N. It is suspended by strings AC and BD. A block P weighing 96N is attached at E, 0.30N from A. The tension force in the string BD has a magnitude.

My work:
Taking torque around AC string
clockwise=counterclockwise
block P + Board force down= BD tension
(0.3m * 96N)+ (.6m * 16N)= BD (1.2m)
38.4= BD(1.2m)
BD= 32N

An 800N man stands halfway up a 5.0m long ladder of negligible weight. The base of the ladder is 3.0m from the wall. Assuming that the wall-ladder contact is frictionless, the wall pushes against the ladder with a force magnitude of:

my work:

cos (theta) = 3m/5m
theta= 53.13 degrees

horizontal components
Ff (friction foce on bottom) - FN (normal force on top) = 0

Ff=FN

vertical components:
Torque taken from top point of ladder
clockwise= counterclockwise
(800N X 2.5X cos(53.1))= FN(5)
FN=240N

Thank you

Was i right for the first problem?

yes.

also from what you wrote....we don't need Cos. I'm sorry I'm confused.

You can do it with the cosine, it gets the same answer. I just figured the distances along the normals from the diagram. Using cosines, you get the same thing.

Torque= force*distance*cosineangle OR
Torque= force*distance perpendicular between the force and point.

An 800N man stands halfway up a 5.0m long ladder of negligible weight. The base of the ladder is 3.0m from the wall. Assuming that the wall-ladder contact is frictionless, the wall pushes against the ladder with a force magnitude of:

my work:

cos (theta) = 3m/5m
theta= 53.13 degrees

horizontal components
Ff (friction foce on bottom) - FN (normal force on top) = 0

Ff=FN

vertical components:
Torque taken from top point of ladder
clockwise= counterclockwise
(800N X 2.5X cos(53.1))= FN(5)
FN=240N
***No. FN*5 is not the torque, Fn*4 is the torque. You need the perpendicular distance. And what happened to friction? Doesnt friction provide a ccw torque?

Summing around top:
cw= ccw
Ff*4 + 800*1.5 = Fv*3

But Fv= 800 , so Ff= 800*1.5/4= 300, but since summing horizontal forces, Ff= Fn, then Fn= 300

check my thinking.

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