A quality engineer tests a concrete support using an ultrasound probe. Two small reflectors embedded in the concrete are 36 mm apart along the path of the pulse. Echoes from the two reflectors arrive at the probe 18 μs18\ \mu\mathrm{s}18 μs apart.
What is the speed of ultrasound in the concrete?
4000 m/s4000\ \mathrm{m/s}4000 m/s
2000 m/s2000\ \mathrm{m/s}2000 m/s
1000 m/s1000\ \mathrm{m/s}1000 m/s
8000 m/s8000\ \mathrm{m/s}8000 m/s