Final answer:
To determine the time to hear an echo, the total distance the sound travels must be divided by the speed of sound. In this case, the echo will be heard approximately 0.176 seconds after the sound strikes an obstacle 30 meters away, with a sound speed of 340 m/s.
Step-by-step explanation:
The question involves calculating the time it takes for an echo to be heard after a sound hits an obstacle. Given that the speed of sound in air is 340 m/s and the obstacle is at a distance of 30 meters, the sound has to travel to the obstacle and back, making the total distance 60 meters. Using the formula time = distance / speed, we can calculate the time taken for the echo to be heard:
time = 60 m / 340 m/s = 0.176 seconds (approximately)
Therefore, the time to hear the echo after the sound has struck the obstacle would be approximately 0.176 seconds