A sensor is fixed to the edge of a circular fish-farm cage of diameter 40 m. It sends an ultrasound pulse through the water along a diameter of the cage towards a shoal of fish. The shoal is 10 m from the opposite edge of the cage. The speed of sound in the water is 1500 m/s.
What is the time between the pulse being sent and the echo from the shoal being detected by the sensor?
0.020 s0.020\ \mathrm{s}0.020 s
0.067 s0.067\ \mathrm{s}0.067 s
0.013 s0.013\ \mathrm{s}0.013 s
0.040 s0.040\ \mathrm{s}0.040 s