As shown in the figure, Figure A is a schematic diagram of a vehicle speed measurement on a highway using an ultrasonic speed tester. The tester emits and receives ultrasonic pulse signals. According

As shown in the figure, Figure A is a schematic diagram of a vehicle speed measurement on a highway using an ultrasonic speed tester. The tester emits and receives ultrasonic pulse signals. According to the signals emitted Analysis: from the question b figure can be seen, send out ultrasonic signal p1 to receive the reflected signal n1 time for: t1 = 12 × s = 0.4 s, at this time, the car from the speedometer distance s1 = × v - t1 = × 340 × 0.4 m = 68 m, the same can be obtained send out the signal p2 to receive the signal n2 time for t2 = 9 × s = 0.3 s, s2 = vt2 = 51 m,

So the car receives p1, p2 two signals between the time the distance forward for:

Δs = 68 m-51 m = 17 m

Set the car running 17 m for t, the car receives the signal to p1 to the tachymeter receives the signal n1 reflected p1 time for t1′ = t′ = 0.2 s, tachymeter received the The car signal by t2′ = 1 s-0.4 s = 0.6 s launch p2, and then by t3 = × 0.3 s = 0.15 s the car received p2, so the car traveled 17 m distance time t = t1′ + t2′ + t3′ = 0.95 s, so the car's speed v ′ = m / s = 17.9 m / s.

Answer: 17 m 17.9 m / s<

Answer: 17 m 17.9 m/s<