M Un cocodrilo se arrastró 25 m hacia la derecha con una velocidad promedio de –1.2 -.
¿Cuántos segundos se arrastró el cocodrilo?

El cocodrilo se arrastró durante 20.833 segundos.

Explanation:

El enunciado presenta omisiones y errores conceptuales. La forma correcta es la siguiente: "Un cocodrilo se arrastró 25 metros hacia la derecha con una  rapidez promedio de 1.2 metros por segundo. ¿Cuántos segundos se arrastró el cocodrilo?"

Consideremos que el cocodrilo tiene un movimiento rectilíneo uniforme, el tiempo requerido para el recorrido se calcula con la siguiente ecuación cinemática:

(1)

Donde:

- Distancia recorrida, en metros.

- Rapidez del cocodrilo, en metros por segundo.

- Tiempo, en segundos.

Si y , entonces el tiempo empleado por el cocodrilo es:

El cocodrilo se arrastró durante 20.833 segundos.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years