Serway & Jewett — Physics and Measurement: Problem 6

A surveyor measures the distance across a straight river by the following method (Fig. P1.6). Starting directly across from a tree on the opposite bank, she walks \( d = 100\text{ m} \) along the riverbank to establish a baseline. Then she sights across to the tree. The angle from her baseline to the tree is \( \theta = 35.0^\circ \). How wide is the river?