Differential Equations of First Order and First Degree 2-79
3. If the temperature of the air is 20°C and the temperature of a
body drops from 100°C to 75°C in 10 min. what will be its tem-
perature after 30 min? When will the temperature be 30°C?
Ans: 46°C, 55.5 min
4. Uranium disintegrates at a rate proportional to the amount pres-
ent at any instant. If m
1
and m
2
gms of uranium are present at
time t
1
and t
2
, respectively. Show that the half-life of uranium is
(
)
2112
[()log 2]/log/.ttmm−
5. The rate at which bacteria multiply is proportional to the instan-
taneous number present. If the original number doubles in 2 hrs,
in how many ...
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