Question

The Law and Order detectives enter a house at 11:30 am and found a man on the floor murdered. They take his body temperature finding to be 91.8 F. The body is taken to the morgue and at 12:30 pm the body temperature is 84.4 F. Using an exponential model for the body temperature, to the nearest minute, what time was he killed. Normal body temperature is 98.6.

Answer 1

Answer:

Time of murder = 10:39 am

Step-by-step explanation:

Let the equation of exponential function representing the final temperature of the body after time 't' is,

f(t) = $a(e)^{nt}$

Here, a = Initial temperature

n = Constant for the change in temperature

t = Duration

At 11:30 am temperature of the body was 91.8°F.

91.8 = $98.6(e)^{nt}$ --------(1)

Time to reach the body to the morgue = 12:30 pm

Duration to reach = 12:30 p.m. - 11:30 a.m.

                              = 1 hour

Therefore, equation will be,

84.4 = $91.8(e)^{n\times 1}$

eⁿ = $\frac{84.4}{91.8}$

ln(eⁿ) = ln(0.9194)

n = -0.08403

From equation (1),

91.8 = $98.6(e)^{-0.08403t}$

$(e)^{0.08403t}=\frac{98.6}{91.8}$

$ln[(e)^{0.08403t}]=ln[\frac{98.6}{91.8}]$

0.08403t = 0.07146

t = 0.85 hours

t ≈ 51 minutes

Therefore, murder was done 51 minutes before the detectives arrival.

Time of murder = 11:30 - 00:51

                          = 10:90 - 00:51

                          = 10:39 am