Recibimos por radio un mensaje del ferry que dice: "estamos a 70km de santa cruz y vamos hacia allí a 60km/h? a) ¿a que distancia de santa cruz estará el ferry dentro de cuarenta minutos?

a)    t = 0.75 s,  b)  t = 2.25 s

Explanation:

The speed of sound is constant in a material medium

           v = 340 m / s

we can use the relations of uniform motion to find the time

          v = x / t

          t = x / v

In the exercise, the observer's distance to the wall is indicated d = 510 m, it also indicates that the shot is fired at the midpoint

          x = d / 2

a) direct sound the distance from the observer to the screen is

           x = 510/2 = 255 m

           t = 255/340

           t = 0.75 s

b) echo sound.

In this case the sound reaches the wall bounces, the distance is

             x = d / 2 + d

             x = 3/2 d

             x = 3/2 510

             x = 765 m

the time is

              t = x / v

              t = 765/340

              t = 2.25 s

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.