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## Homework Statement

A food packaging factory is moving soup through a [itex]0.075 m[/itex] diameter pipe when an obstruction occurs in the pipe. An ultrasound probe, connected to an oscilloscope, is moved along the pipe to find the obstruction (

*Figure 1*). The oscilloscope trace is shown below

(

*Figure 2*).

*Figure 1*:

*Figure 2*:

Oscilloscope time base = [itex]20 \times 10^{-6} s \ cm^{-1}[/itex]. On figure 2, pulse A is the outgoing signal from the probe and pulse B is the reflected signal from the other side of the pipe, Calculate the speed of the ultrasound in the liquid in the pipe.

## Homework Equations

[itex]v = \frac{s}{t}[/itex]

## The Attempt at a Solution

I understand which formula to use but I am struggling to obtain values from the graph shown. The wording has confused me. I would have thought that the time is [itex](6) \times (20 \times 10^{-6})[/itex] but it is incorrect.

The correct calculation is:

[itex]v = \frac{s}{t}[/itex]

[itex]= (150 \times 10^{-3} \ \mathrm{(m)}) \div (132 \times 10^{-6} \ \mathrm{(s)})[/itex]

How did the mark scheme obtain the value for the calculations? Thanks in advance.