Answer:
Explanation:
Given
rope makes an angle of 
Mass of sled and snow is m
Normal Force 
applied Force is F
as Force is pulling in nature therefore normal reaction is given by

Also 


-------1
---------2
Squaring 1 & 2 and then adding


Substitute value of F in 1


Answer:
160J
Explanation:
Given force = 8N and total distance = 20 meters
Workdone = force x distance
= 8 x 20
= 160J
Therefore, workdone by Riley in pulling the hoover is 160J
These forces form a force pair. Use Newton's third law, and you see that the trailer pulls back at with the same force. The answer is d.