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The rate of decay in the mass, M, of a radioactive substance is given by the differential equation dM dt equals negative 1 times k times M , where k is a positive constant. If the initial mass was 150g, then find the expression for the mass, M, at any time t

Sagot :

Using separation of variables, it is found that the expression for the mass, M, at any time t, is given by:

[tex]M(t) = 150e^{-kt}[/tex]

What is separation of variables?

In separation of variables, supposing a differential equation in the format [tex]\frac{dy}{dx}[/tex], we place all the factors of y on one side of the equation with dy, all the factors of x on the other side with dx, and integrate both sides.

In this problem, the differential equation is:

[tex]\frac{dM}{dt} = -kM[/tex]

Then, applying separation of variables:

[tex]\frac{dM}{M} = -k dt[/tex]

[tex]\int \frac{dM}{M} = \int -k dt[/tex]

[tex]\ln{M} = -kt + C[/tex]

[tex]M(t) = M(0)e^{-kt}[/tex]

The initial mass is of M(0) = 150, hence:

[tex]M(t) = 150e^{-kt}[/tex]

More can be learned about separation of variables at https://brainly.com/question/14318343