Why Is My Calculated Speed of Sound Incorrect?

[Astonix]

Homework Statement

We have to prove the speed of sound using a ultra-sound emitter, connected to EasySense software which records the speed for it to travel to surface and back. Known data - Speed of sound is 337 metres a second at 20 degrees celsius. Also, the distance covered is, 3.4m or 6.8m there and back. The time is 0.010837 micro seconds. Micro-seconds are 1 x 10^-6. All answers must be given with a +- .

Homework Equations

Speed = Distance / Time

The Attempt at a Solution

Time: 10897 +- 14 (microsecs)
Dist: 6.8 +- 0.014 (metres)

Convert microseconds into seconds. 10897 / 1000 and then /1000 again.
= 0.010897 seconds

Speed = 6.8 / 0.010897 = 624.024961 metres per second.

Obviously, this is nearly double the actual speed of sound. Was I not meant to double the distance? But I'm pretty sure the time is for there and back so double distance was needed. Have I forgotten anything? Of course, there is a chance the Ultrasound was reflecting from a place not wanted, causing the distance to not be true.

Help much appreciated.

 

[AC130Nav]

Homework Statement

We have to prove the speed of sound using a ultra-sound emitter, connected to EasySense software which records the speed for it to travel to surface and back. Known data - Speed of sound is 337 metres a second at 20 degrees celsius. Also, the distance covered is, 3.4m or 6.8m there and back. The time is 0.010837 micro seconds. Micro-seconds are 1 x 10^-6. All answers must be given with a +- .

Homework Equations

Speed = Distance / Time

The Attempt at a Solution

Time: 10897 +- 14 (microsecs)
Dist: 6.8 +- 0.014 (metres)

Convert microseconds into seconds. 10897 / 1000 and then /1000 again.
= 0.010897 seconds

Speed = 6.8 / 0.010897 = 624.024961 metres per second.

Obviously, this is nearly double the actual speed of sound. Was I not meant to double the distance? But I'm pretty sure the time is for there and back so double distance was needed. Have I forgotten anything? Of course, there is a chance the Ultrasound was reflecting from a place not wanted, causing the distance to not be true.

Help much appreciated.

You have very different times in 1 and 3 above. Could you also have misunderstood the distance?