Extreme heat applied to a colony of microorganisms causes the size P of the colony, measured in grams, to decrease according to the exponential decay model dP/dt=−0.4P, where the time t is measured in hours. The size Q of a second colony of microorganisms, also measured in grams, decreases at the constant rate of 1 gram per hour according to the linear model dQ/dt=−1. If at time t=0 the first colony has size P(0)=2 and the second colony has size Q(0)=3, at what time will both colonies have the same size?

Respuesta :

Step-by-step explanation:

dP/dt = -0.4P

Separate the variables and integrate.

dP/P = -0.4 dt

ln|P| = -0.4t + C

P = Ce^(-0.4t)

Use initial condition to find C.

2 = C^(0)

C = 2

P = 2e^(-0.4t)

dQ/dt = -1

Integrate.

Q = -t + C

Use initial condition to find C.

3 = 0 + C

C = 3

Q = -t + 3

Set the two equal.

2e(-0.4t) = -t + 3

Use a calculator to find t.

t = 2.156

The populations have the same size after 2.156 hours.

The populations both colony have the same size after 2.156 hours.

Given that,

The size P of the colony, measured in grams, to decrease,

According to the exponential decay model dP/dt=−0.4P,

Where the time t is measured in hours.

The size Q of a second colony of microorganisms, also measured in grams, decreases at the constant rate of 1 gram per hour

According to the linear model dQ/dt=−1.

If at time t=0 the first colony has size P(0)=2 and the second colony has size Q(0)=3,

We have to determine,

What time will both colonies have the same size.

According to the question,

[tex]\dfrac{dp}{dt} = 0.4p[/tex]

Separate the variables and integrate,

[tex]\dfrac{dp}{p} = 0.4 dt\\\\integrate\ both \ the \ sides ,\\\\\int\dfrac{dp}{p} = \int0.4dt\\\\ln|p| = 0.4t+c\\\\Taking \ exponential \ both \ sides\\\\P = c.e^{(0.4t)}[/tex]

Using initial condition to find C.

[tex]2 = c^{0} \\\\c = 2[/tex]

Substitute c = 2 in the equation,

[tex]P = 2.e^{(0.4t)}[/tex]

Again, integrate the second function,

[tex]\dfrac{dQ}{dt} = -1\\\\On \ integrating \ both \ the \ sides\\\\\int dQ = \int -1.dt\\\\Q = -t +c \\[/tex]

Use initial condition to find C.

[tex]3 = 0+c[/tex]

Then ,

[tex]Q = -t +3[/tex]

On comparing both the equation to get the value of t,

[tex]2. e^{(0.4t)} = -t+3\\\\t = 2.156[/tex]

Hence, The populations both colony have the same size after 2.156 hours.

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