Question

1.     A hiker determines the length of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.5 s after shouting. Estimate the length of the lake.

Answer 1

The distance traveled by the sound can be found as follows:

$$d=vt.$$

From the other hand, the total distance from the hiker to the cliff and back equals:

$$d=2l.$$

Then, we get:

$$2l=vt,$$ $$l=\dfrac{vt}{2}=\dfrac{343\ \dfrac{m}{s}\cdot2.5\ s}{2}=430\ m.$$