Assume that the rate of evaporation for water is proportiona

Annette Sabin

Annette Sabin

Answered question

2021-12-29

Assume that the rate of evaporation for water is proportional to the initial amount of water in a bowl. If Jill places 1 cup of water outside and notices that there is 12 cup of water 6 hours later. Can she use a differential equation to find when there is no water left?

Answer & Explanation

Gerald Lopez

Gerald Lopez

Beginner2021-12-30Added 29 answers

Step 1:Define differential equation
Here, given that rate of change of evaporation is proportional to the initial amount of water.
Therefore, we can model a differential equation to find the actual amount of evaporation.
In the following way we can describe the model.
Step 2: Find equation
Let say, rate of change of evaporation is dedt.
Also consider that the initial amount of water was w.
According to question:
dedtw.
Therefore, by the property of proportion:
dedt=k.w, where k is a constant.
By using integration:
de=kwdt
Solving it we get:
e=kwt+C, C is arbitrary const.
So, et=kw+C1,where C1=Ct.
Now, w=1,e=12,t=6,
Therefore, 126=k.1+C1
k+C1=112.
When w=1,t=0:e=0
Therefore, C1=0
Step 3
Therefore, k=112.
Therefore, the equation can be written as:
e=wt12.
Annie Gonzalez

Annie Gonzalez

Beginner2021-12-31Added 41 answers

We know that rate of change the volume of water w, is proportional to the volume of water currently in the glass, is we know dwdtw.
dwdt=kw
This is separable differential eq. We separate integrate to find dWdt=kWdWW=kdtdww=kdt
lnw=kt+cw(t)=Aekt
Where we wrote A=ec note that is the initial volume of water. We know that half of the water remains after 7 hours, is wA=12,when t=7. And so ek(7)=12
7k=ln(12)
k=17ln(12)=0.09902
Note that this is negative because this is an example of exponential decay.
We have A=8oz, so water eq is
w(t)=8e0.099oz
So after 9hrs, the remaining volume of water is w(9)=8e0.099oz(9)
w(9)=3.28oz.
Vasquez

Vasquez

Expert2022-01-09Added 669 answers

dedtw.
dedt=k.w, where k is a constant.
de=kwdt
e=kwt+C, C is arbitrary const.
So, et=kw+C1,where C1=Ct.
Now, w=1,e=12,t=6,
Therefore, 126=k.1+C1
k+C1=112
w=1, t=0: e=0
C1=0
Step 3
k=112.
e=wt12.

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