Question

A boat travels at 30 mph for a huge, solid cliff that is about 3,000 meters away. When the horn on the boat makes a toot, you can hear the initial sound directly from the horn and also an echo from the cliff wall some time later. How does the frequency of the echo compare with the frequency of the horn before the ship moved?
Group of answer choices

The frequency of the echo is slightly increased.

The frequency of the echo is slightly decreased.

The frequency is unchanged.

Not enough information to determine.

Answer 1

Answer:The frequency of the echo is slightly decreased

Explanation:

Given

speed of boat $=30\ mph$

cliff is $3000\ m$ away

when boat is still , suppose t is the time taken by the echo to reach observer on the boat

But as soon as boat starts moving  the distance between cliff and boat decreasing and time for echo to reach observer also decreases

and we know $time \propto \frac{1}{frequency}$

therefore frequency of the echo slightly decreased.