Answer:
a) 238U, 40K and 87Rb, b) 235U and to a lesser extent 40K , c) he 235U,
d) possibility is 14C , e)this period would be ideal for 14C , f) 14C should be used since it is the one with the least average life time, even though the measurements must be very careful
Explanation:
One of the applications of radioactive decay is the dating of different systems.
To do this, the quantity of radioactive material in a meter is determined and with the average life time, the time of the sample is found.
Let's write the half-life times of the given materials
87Rb T ½ = 4.75 1010 years
147Sm T ½ = 1.06 1011 years
235U = 7,038 108 years
238U = 4.47 109 years
40K = 1,248 109 years
14C = 5,568 103 years
we already have the half-life of the different elements given
a) meteors. As these decomposed in the formation of the solar system, their life time is around 3 109 to 5 109 years, so it is necessary to look for elements that have a life time of this order, among the candidates we have 238U, 40K and 87Rb if these elements were at the moment of the formation of these meteors, there must still be rations in them, instead elements 14C already completely adequate
b) rock. The formation period is 4.20-108 years, therefore one of the most promising elements is 235U and to a lesser extent 40K since it is more abundant in rocks. The other elements with higher life times have not decayed and therefore will not give a true value and the 14C is completely decayed
c) volcanic ash. Formation time 6107 years, the only element that has the possibility of having a count is the 235U, the others have a life time so long that they have not decayed and the 14C is complete, unbent
d) scarp of an earthquake formation time 5 101 years, The only one that has any possibility is 14C even when it has declined very little, all the others, you have time to long that has not decayed
e) INCA excavation. The time of this civilization is about 10000 to 500 years (104 to 5 102 years), we see that this period would be ideal for 14C since it has some period of cementation, the others have not decayed
f) Tree in Blepharitis. 14C should be used since it is the one with the least average life time, even though the measurements must be very careful because of a period of disintegration. We have such a long time that they have not decayed
. Calling h its height at t=0, the height at time t is given by
the grapefruit hits the ground, so h(0.75 s)=0. If we substitute these data into the equation, we can find the initial height h of the grapefruit:
is the initial speed of the grapefruit. Substituting t=0.75 s, we find the speed when the grapefruit hits the ground: