why is the answer wrong and how to correct it 00000996650297

why is the answer wrong and how to correct it?

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Solution

The force opposing the movement of a machine up a slope is known as GRADE RESISTANCE. It acts against the total weight of the machine. i.e power required to move a machine on an upward slope is more, Hence its sign is to be taken PLUS.

GRADE ASSISTANCE :

The force assists the movement of a machine down a slope is known as GRADE ASSISTANCE, It acts along the total weight of machine i.e. power required to move a machine on downward slope is less, hence its sign is to be taken MINUS.

In the above problem the machine is returning empty (i.e. moving downward) from fill to cut Therefore the sign of GRADE ASSISTANCE will be -ive.

Fill rate = 1553 lb/tn

cut rarte = 1443 lb/tn

Resistance = 1553 - 1443 = 110 lb/tn

Hence Grade Resistance or Haul Grade or Grade from cut to fill = +110/2000 =+ 0.055 = + 5.5%

and Grade Assistance or Return Grade or grade from fill to cut = -110/2000 = - 0.055 = - 5.5%