Question

From the top of a vertical cliff 75.0m high, forming one bank of a river, the angles of depression of the top and bottom of a vertical cliff which forms the opposite bank are 22° and 58° respectively. Determine the height of the second cliff and width of the river

Answer 1

a. 46.9 m b. 56.1 m

Explanation:

a. Width of the river

The angle of depression of the bottom of the second vertical cliff from the first vertical cliff = angle of elevation of the top of the first vertical cliff from the bottom of the second vertical cliff = 58°.

Since the height of the vertical cliff = 75.0 m, its distance from the other cliff which is the width of the river, d is gotten from

tan58° = 75.0 m/d

d = 75.0/tan58° = 46.87 m ≅ 46.9 m

b. Height of the second cliff

Now, the difference in height of the two cliffs is gotten from

tan22° = h/d, since the angle of depression of the top of second cliff from the first cliff is the angle of elevation of the top of the first cliff from the second cliff = 22°

h = dtan22° = 18.94 m

So, the height of the second cliff is h' = 75.0 - h = 75.0 m - 18.94 m = 56.06 m ≅ 56.1 m