A detective discovers a murder victim in a room at the Marriott Marquis Hotel at 9:15 pm on Friday night. Immediately, the temperature of the body is recorded as being 78 °F. The programmable thermostat has been set to 70 °F for the last week. What was the time of death?

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A detective discovers a murder victim in a room at the Marriott Marquis Hotel at 9:15 pm on Friday night. Immediately, the temperature of the body is recorded as being 78°F. The programmable thermostat has been set to 70°F for the last week. What was the time of death?

Newton's Law of Cooling is an exponential equation, which describes the cooling of a warmer object to the cooler temperature of the environment. Specifically, we write this law as:

\[ T(t) = T_e + (T_0 - T_e) e^{-kt} \]

where \( T(t) \) is the temperature of the object at time \( t \), \( T_e \) is the constant temperature of the environment, \( T_0 \) is the initial temperature of the object, and \( k \) is a constant that depends on the material properties of the object. To solve this exponential equation for \( t \), you will need to use logarithms. This equation can be rearranged to:

\[ \frac{T(t) - T_e}{T_0 - T_e} = e^{-kt} \]

**Tip:** To organize our thinking about this problem, let’s be explicit about what we are trying to solve for. We would like to know the time at which a person died. In particular, the investigator arrived on the scene at 9:15 pm, which is \( t \) hours after death. The temperature of the body was found to be 78°F. Assume \( k = 0.1335 \) and the victim’s body temperature was normal (98.6°F) prior to death. Show all work.
Transcribed Image Text:A detective discovers a murder victim in a room at the Marriott Marquis Hotel at 9:15 pm on Friday night. Immediately, the temperature of the body is recorded as being 78°F. The programmable thermostat has been set to 70°F for the last week. What was the time of death? Newton's Law of Cooling is an exponential equation, which describes the cooling of a warmer object to the cooler temperature of the environment. Specifically, we write this law as: \[ T(t) = T_e + (T_0 - T_e) e^{-kt} \] where \( T(t) \) is the temperature of the object at time \( t \), \( T_e \) is the constant temperature of the environment, \( T_0 \) is the initial temperature of the object, and \( k \) is a constant that depends on the material properties of the object. To solve this exponential equation for \( t \), you will need to use logarithms. This equation can be rearranged to: \[ \frac{T(t) - T_e}{T_0 - T_e} = e^{-kt} \] **Tip:** To organize our thinking about this problem, let’s be explicit about what we are trying to solve for. We would like to know the time at which a person died. In particular, the investigator arrived on the scene at 9:15 pm, which is \( t \) hours after death. The temperature of the body was found to be 78°F. Assume \( k = 0.1335 \) and the victim’s body temperature was normal (98.6°F) prior to death. Show all work.
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