Calculating Force R: Distributed Load Homework

[princejan7]

Homework Statement

http://postimg.org/image/7vpxry28t/


Can someone explain how they calculated the force R representing the distributed load?
Did they even make use of the value "800N/m" from the question?

 

[SteamKing]

The calculation for R is included in the solution section. You don't need to use the 800 N/m unless you calculated the value of R using the formula for the area of a trapezoid:

R = (0.6/2)*(400 + 800) = 360 N

I think they are trying to show how to break up a trapezoidal load into a constant distributed load and a triangular load.

 

[Chestermiller]

Homework Statement

http://postimg.org/image/7vpxry28t/



Can someone explain how they calculated the force R representing the distributed load?
Did they even make use of the value "800N/m" from the question?

Yes, they used the 800, but they obtained the force R result a stupid (IMHO) way. The way I would have done it would have been to note that the average distributed load over the length of the member is 600 N/m. If we multiply that by the length of the member (0.6), we get 360 N. They did something like the following: the minimum distributed load over the length of the member is 400 N/m, so this contributes 400 (0.6) = 240N. Over and above that, the remainder of the load varies from 0 at the left end to 400 at the right end (400 to 800, minus the 400 already accounted for). The average of this excess is (0+400)/2 = 200. The load contribution of this excess is (400/2)(0.6)=120N. The total load R is again 360 N. As I said, their method is kinda stupid.

Chet

 

[princejan7]

thanks