Explanation:
To determine the length of cable needed for the zip line, we first need to calculate the horizontal distance between the two trees. Let's assume that the distance between the trees is d feet. We also need to calculate the vertical change in height of the cable between the two trees. Let's assume that the height difference is h feet.
Given the slope constraint, we know that for every 6 to 8 feet of vertical change, we need 100 feet of horizontal change. This means that the slope of the zip line should be between 6/100 and 8/100. We can use this information to set up a proportion:
vertical change / horizontal change = slope
h / d = 6/100 or h / d = 8/100
Solving for d in each of these equations, we get:
d = h / (6/100) = 100h / 6 = 50h / 3 (for the minimum slope of 6/100)
d = h / (8/100) = 100h / 8 = 25h / 2 (for the maximum slope of 8/100)
To account for the required 5% slack in the line, we need to increase the length of the cable by 5%. This means that the actual length of cable needed is:
L = 1.05d + 12
where 12 feet represents the 6 extra feet of cable needed at each end to wrap around each tree.
Substituting the expressions for d that we derived earlier, we get:
L = 1.05(50h/3) + 12 = (175h/6) + 12 (for the minimum slope of 6/100)
L = 1.05(25h/2) + 12 = (131h/40) + 12 (for the maximum slope of 8/100)
Therefore, the total length of cable needed for the zip line depends on the height difference between the trees and the desired slope of the line. For example, if the height difference is h = 50 feet and we want to use the minimum slope of 6/100, then the total length of cable needed would be:
L = (175(50)/6) + 12 = 1462.5 feet
If we want to use the maximum slope of 8/100, then the total length of cable needed would be:
L = (131(50)/40) + 12 = 73.2 + 12 = 85.2 feet
Note that these values are approximations and do not take into account factors such as the weight of the rider or the tension of the cable.