You are in a canyon and yell across. It takes 4 seconds for the
echo to come back to you. How wide is the canyon?

Width = 680 [m]

Explanation:

To solve this problem we must know the speed of sound in the air, conducting an internet search, we find that this speed has a value of v = 340 [m/s].

We apply the following kinematic equation, which relates space to time, to define speed.

v = x /t

where:

x = distance [m]

t = time [s]

v = velocity [m/s]

Now replacing:

x = 340 * 4

x = 1360 [m]

But the width of the cannon is calculated when the sound wave hits the wall of the canyon, so this width is half the distance.

Width = 1360 / 2 = 680 [m]

b.a device that inputs heat into a cool object