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2 years ago

13

A rock once contained 1.0 mg of uranium-238, but now contains only 0.25 mg. Given that the half-life for uranium-238 is 4.5 x 10

^9 (4.5 billion) years, how old is the rock?

1 answer:

Darina [25.2K]2 years ago

5 0

Answer:

9 x 10 ^9 yrs ( 9 billion years <=====older than Earth !)

Explanation:

.25 = 1.0 (1/2) ^n

.25 / 1.0 = = (1/2 )^n

log .25 = n log 1/2

n = 2 half lives

2 * 4.5 x 10^9 = 9 x 10 ^ 9 yrs

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Estimate (a) the maximum, and (b) the minimum thermal conductivity values (in W/m-K) for a cermet that contains 83 vol% carbide

velikii [3]

Answer:

k_max = 31.82 w/mk

k_min = 17.70 w/mk

Explanation:

a) the maximum thermal conductivity is given as

$k_{max} = k_m*v_m + k_p*v_p$

where k_m is thermal conductvitiy of metal

k_p is thermal conductvitiy of carbide

v_m = proportion of metal in the cement = 0.17

v_p = proportion of carbide in the cement = 0.83

= 66*0.17 + 28*0.83

k_max = 31.82 w/mk

b) the minimum thermal conductivity is given as

$k_{min} = \frac{k_{carbide}* k_{metal}}{k_{metal} v_{carbide} +k_{metal} v_{carbide}}$

= \frac{28+66}{28*0.17 +66*0.83}

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