Resoluçao:

distância entre os dois amigos 60 m.

distância entre o amigo e o obstáculo 40 m

x² = 40² + 30²                                                                    50 + 50 = 100 m

x² = 1600 + 900                                                                  100 - 60 = 40 m

x² = 2500                                                                             v = s/t

x² = √2500                                                                            340 = 40/t

x = 50 m                                                                                 t = 40/340

                                                                                                t = 0,12 s

Resposta: 0,12