Help needed on statics, and also to check my answers

Too small give me a bigger image! YIKES

 

ahhhhhhhh my eyes! thanks

 

For Tension in number two i get 3,678.75, Just cut the ropes, then there is 4T going up and 1500*9.81 going down, and solve for t, very simple.
The mechanical advantage you provide is 3,678.75 to lift up 1500*9.81 or 14715/3678.75 = 4 times. But im not sure how that is defined, so i may be wrong. A mechanical advantage of 4k just doesnt make sense to me, sorry. Ah, I read what you wrote, you have good numbers but assigned them wrong. 14,715 is the weight of the block no the tension, that 3k value is the tension, and 4 is right for the advantage.

 

Number 3 is simple as well. For a square, the force acts at the center along the x axis, so the total force is F= 5kn/m * 3m = 15kN acting at x=1.5 m.

Now for the triangle, the force acts 1/3 from the height of the trangle, or 2/3 of x from the other direciton. so the total force is again the area, so its F = (5kn/m* 3m )/2
(the area of that triangle). and it acts a distance 2/3 rds away, (BUT add in the distance for the rectangle too!) so its [(2/3) *3 ] +3, the +3 is because of the distance due to the rectangle! Now you have two forces at two distances, and you have to add them, and find the resultant distance this force acts, by summing the moments about the pin. (But first find the reaction of the smooth roller!) I Hope that helps you. I wont do it for you though.

 

NO! Weight = 1500*9.81, thatsthe WEIGHT of the block. The tension is what holds it up. Look, just cut the ropes so that its 4 ropes magically pointing up. Do you see what i mean?
....T........T........T........T
.../\...... /\......./\...... /\
__|_____|_____|_____|
|.................W ...........|
|..................|............|
|.................\/............|
------------------------

So 4T acts UP, and the Weight W, acts DOWN.

Now find what T is, its 1/4 the total weight, obviously.

 

do you get what im saying?

 

Yeah, but do you understand what im trying to show you? If its not clear let me know.

 

You have to go back and read about centroids of various areas. This is the location that works when you find the centrioid, or geometric center of a shape based on a mathematical definition. If you have a right triangle, the centroid is ALWAYS 1/3 away form the base so graphically:
.................................../..|
................................./....|
.............................../......|
............................./ .......|
.......................... /......... |
........................../.......... |
......................../.............|
......................./..............|
.................... /................|
..................../ -----------|
........................./\
........................ |<-1/3->|

So that distance of the centroid is 1/3 from the side with the |'s, or 2/3s away from the side with the /, get it?