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]

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )