An Object Cools at a Rate (Measured In ${ } ^ { \circ } \mathrm { C } / \mathrm { min }$

question 81

Multiple Choice

An object cools at a rate (measured in ${ } ^ { \circ } \mathrm { C } / \mathrm { min }$ ) equal to $k$ times the difference between its temperature and that of the surrounding air. Suppose the object takes 10 minutes to cool from 60 $^\circ$ C to 40 $^\circ$ C in a room kept at 20 $^\circ$ C. Find the value of $k$ .

• A) \(e ^ { - 20 }\)
• B) \(\ln 2\)
• C) \(10 e ^ { - 20 }\)
• D) \(40 \ln 10\)
• E) \(\frac { 1 } { 2 }\)
• F) \(e ^ { - 1 / 20 }\)
• G) \(\frac { 1 } { 10 } \ln \frac { 1 } { 2 }\)
• H) \(60 \ln \frac { 1 } { 2 }\)

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