Moment in beam

1. The problem statement, all variables and given/known data
refer to the circled part , i dont understand the author's working .



2. Relevant equations


3. The attempt at a solution
I think it should be 450x - 150(4-x) -30092)(x-1) , correct me if i'm wrong . (taking moment about x ) ....

 

is the author wrong , coz the distributed load start from R1 to 2m from R1 ...

 

why ? i still dont understand , i can only understand the 450x , why should be -0.5(300)(x^2) +0.5(300)[(x-2)^2 ]

 

why shouldnt it be 450x - 150(4-x) -300(0.5)(2)(x-1) ??

 

i dont understand why it is -0.5(300)(x^2) +0.5(300)[(x-2)^2 ] , can you explain ?

 

why it's 0.5(300)(x^2) ? the 300N/m only 'defined ' from R1 to 2m from R1, am i right ? why shouldnt it be 0.5(300)(2)(x-2) instead? as you said , after 2m , net distributed load is zero

 

the location of 300n/m is at R1 and extend to 2m from R1, so ,the EIy" should be = 450x-300(2)(x-1) ???
why there's -0.5(300)(x^2) +0.5(300)( (x-2)^2 )????
I'm confused

Or do you mean the 300(X) force still exist at X >2?

 

bump