Question 1 Report
A sound pulse sent vertically downwards into the earth is reflected from two different layers of the earth such that echoes are heard 1.2s and 1.4s. Assuming speed of the pulse is 2000ms-1, calculate the distance between the layers.
When the sound pulse is sent vertically downwards into the earth, it is reflected from the two layers and returns back to the surface. The time interval between the two echoes is the time taken by the pulse to travel from the first layer to the second layer and back. Let's assume that the distance from the surface to the first layer is 'd' meters and the distance between the first and second layer is 'x' meters. The total distance covered by the pulse would be equal to the sum of the distance travelled to reach the first layer, the distance travelled between the two layers, and the distance travelled to return to the surface. Total distance = d + 2x Using the formula for speed, distance and time, we can express the time taken for the pulse to travel to the first layer and back as: 2d/2000 Similarly, the time taken for the pulse to travel to the second layer and back can be expressed as: 2(d + x)/2000 Given that the time interval between the two echoes is 0.2s, we can set up the following equation: 2(d + x)/2000 - 2d/2000 = 0.2 Simplifying this equation, we get: d + x - d = 200 x = 200m Therefore, the distance between the two layers is 200m. Thus, option A is the correct answer.