The temperature T(t) of a body at time t=0 is 160 F and it decreases continuously as per the differential equation dTdt=-K(T-80), where K is a positive constant. If T(15)=120 F, then T(45) is equal to
- 90 F
- 85 F
- 80 F
- 95 F
Answer
(1) 90 F
Solution
dTT-80=-K dt (T-80)=-Kt+C
t=0, T=160 T-80=80e-Kt
T(15)=120 40=80e-15K e-15K= 12
T(45)=80+80 (e-15K )3=80+80 18=90
Answer: (1)