How Does the Weight at Point E Change When Rod AB Moves Horizontally?

[chawki]

Homework Statement

In the figure between AB is an upright rigid rod and flexible access to B from a rope which passes around the points C and D are located in the rollers for spot through the point E, where the rope is attached to weight.

Homework Equations

How much in section E, this weight will increase when the rod AB be translated into a horizontal plane

The Attempt at a Solution

I really don't get it..any hints?

 

[Piyu]

What are we trying to find here? tension in rope?

I don't see how the weight will increase by moving the rod down. In fact, it may drop seeing the elevation might change if u want to consider the minute gravity drop.

 

[tiny-tim]

hi chawki!

i'm confused …

is this just a geometry problem, to find how much higher M goes if the rope goes straight from C to the bottom of that arc, instead of only from C to B?

 

[chawki]

hi chawki!

i'm confused …

is this just a geometry problem, to find how much higher M goes if the rope goes straight from C to the bottom of that arc, instead of only from C to B?

Hello Tiny-tim :shy:
Actually it will go from B to the bottom, and yes it's probably to find how much higher that mass will go

 

[tiny-tim]

then that's just subtracting one side of the triangle from another, isn't it?

 

[Piyu]

If its the new heigth of the mass.

Lets call the tip of the rod when it's down F. the answer would be FC - BC

u can find the length of FC by using pythaegaros, u got AC and AF(AB)

 

[chawki]

Ok guys I'm lost...what triangle?

 

[Piyu]

using the tip of the rod as F, the triangle would be FCA when the rod is horizontal.

 

[chawki]

Like this ?

 

[Piyu]

Yep and the amount E rises will simply be the difference between the tip of the rod and point C in both scenarios.

 

[chawki]

Ok, if i get it right, the answer would be like this:
(0.5+x)²=2.5²+2²
we solve the equation x²+x-10=0
Delta=41
x₁=-3.70 (it can't be because it's a negative value)
x₂=2.70
so x=2.7m.

 

[chawki]

am i right?

 

[tiny-tim]

In the figure between AB is an upright rigid rod and flexible access to B from a rope which passes around the points C and D are located in the rollers for spot through the point E, where the rope is attached to weight.
…
How much in section E, this weight will increase when the rod AB be translated into a horizontal plane

The question seems to be asking for the difference between the lengths CF and CB.

That's x = √(2.5²+2²) - 0.5

That's the same as your equation…

Ok, if i get it right, the answer would be like this:
(0.5+x)²=2.5²+2²
we solve the equation x²+x-10=0 …

… except for some reason you've turned it into a quadratic equation ……

why?? ​

 

[chawki]

i just applied pythagore law

 

[tiny-tim]

i just applied pythagore law

yes, your first line was Pythagoras' law, but then you should just have taken the square root (that gets you my equation), not made a quadratic out of it

 

[chawki]

but what do you mean ?
the point is the find x, isn't ?

 

[tiny-tim]

yes, but quickly …

That's x = √(2.5²+2²) - 0.5

​