AP Calculus ABeasymcq1 pt

A cup of coffee cools at a rate proportional to the difference between its temperature TT and the surrounding room temperature of 70F70^\circ\mathrm{F}. Which differential equation models this situation, where k>0k>0?

A.dTdt=k(T70)\dfrac{dT}{dt} = -k(T-70)
B.dTdt=k(T70)\dfrac{dT}{dt} = k(T-70)
C.dTdt=k(70T)\dfrac{dT}{dt} = -k(70-T)
D.dTdt=kT\dfrac{dT}{dt} = -kT

Explanation

Core Concept

The rate of change is proportional to the difference T70T-70, and cooling makes dTdt\dfrac{dT}{dt} negative when T>70T>70, so the negative sign is required.

Correct Answer

AdTdt=k(T70)\dfrac{dT}{dt} = -k(T-70)

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