Physics, please help me

The speed of sound is about 340 m/s. Assume that when the motion detector emits an ultrasonic pulse, it must detect the reflected pulse before it can emit its next pulse. Assuming that the length of the air track is about 2 meters, what is the maximum number of pulses per second that the motion detector can emit for measuring distance?

Given:
v = 340 m/s
d = 2 m
t = ?

d = vt
t = d / v
t = 2 m / 340 m/s
t = .0058 s

But the question is asking the time in pulses per second which I don't know how to obtain.

first, the distance the pulse must travel is 4 meters as it must go out and back before it is detected.

assuming your math is correct, the time for it to travel 4 m is twice what you have or .0116 seconds

so the motion detector must wait .0116 seconds before emitting the next pulse. The pulse repitition rate is 1/.0116.....whatever that happens to be....

It's going to detect the reflected pulse... meaning that if it hits the wall of the air track on the opposite (2m away) it's going to reflect back and travel another 2m before hitting the motion detector

v = 340m/s
d=4m
t= 0.012 s

1 second over 0.012s = ~83.33
so about 83 pulses per second can be emitted.

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