The impression of sound lasts on the eardrum for 1/10 of a second the second sound travels a distance 332(m/s) x 1/10s = 33.2m. Thus, the minimum distance between the source of sound and the reflecting body should be 33.2/2 = 16.6m.
As the distance 10m is far less than 16.6m, therefore the ear cannot make out when the original sound had died and echo has been received. Thus, no echo is heard.
