Answer:
work done lifting the bucket (sand and rope) to the top of the building,
W=67.46 Nm
Explanation:
in this question we have given
mass of bucket=20kg
mass of rope=
height of building= 15 meter
We have to find the work done lifting the bucket (sand and rope) to the building =work done in lifting the rope + work done in lifting the sand
work done in lifting the rope is given as, 
= ..............(1)
..............(1)
= 
=22.5 Nm
work done in lifting the sand is given as, 
 .................(2)
.................(2)
Here,
F=mx+c
here,
c=20-18
c=2
m=
m=.133
Therefore,

Put value of F in equation 2


Therefore,
work done lifting the bucket (sand and rope) to the top of the building,
W=22.5 Nm+44.96 Nm
W=67.46 Nm
 
        
             
        
        
        
My calculations state, not rounding, the mass is 1.8
        
             
        
        
        
Then the force will also be doubled
        
             
        
        
        
When an object moves its length contracts in the direction of motion. The faster it moves the shorter it gets in the direction of motion. 
The object in this question moves and then stops moving. So it's length first contracts and then expands to its original length when the motion stops. 
The speed doesn't have to be anywhere near the speed of light. When the object moves its length contracts no matter how fast or slow it's moving.
        
             
        
        
        
D. used by the entire scientific community
B.  more accurate system of measurement