1. In the following, represent the situation pictorially and deduce the governing 1st order differential equations and initial condition for the quantity in question.

a) A tank, containing 300 gallons of pure water initially, is emptied out in the following fashion. A salt solution of concentration ½ lb of salt per gallon is allowed to enter the tank at a constant rate and the well stirred mixture is emptied at twice that rate. The amount of time it takes to drain the tank completely is 60 minutes. The quantity in question is the amount of salt in the tank at any time before it runs dry.

b) A trapped styrofoam sphere of radius "a" and density rho_0 is released from a submerged object and rises vertically from rest in a fluid of density rho_1 > rho_0 . Assume that the fluid medium offers resistance to this sphere proportional to the instantaneous speed (magnitude of the velocity) of the latter and acting in a direction to oppose motion. Further consider the acceleration due to gravity to be a constant, g, and the proportionally constant of resistance equal to k>0. The quantity in question is the velocity of rising sphere as a function of time.

This solution provides an example of how to convert a word problem into a differential equation with an initial condition. Two examples are shown: the first is a mass balance on a vat of salt water with inlet and outlet; the second is a motion problem (kinematics) involving buoyancy. Solution includes hand-drawn diagrams and detailed explanations in pdf file format.

... particle upon time t obeys the differential equation: dv/dt ... derivative is 1, therefore this is a first order equation. ... If we set then the equation becomes: (2.1 ...

... Next we set t=0, and , again we have to first get by ... Now, setting t=0, and gives ...First of all you should notice that the two differential equations we need to ...

... Since D is a diagonal matrix, we get a set of decoupled equations: ... 2. Solve a system of two non-homogeneous first order differential equations using matrices. ...

... (2) As the initial condition (i1) sets x(t_1 )=0 ...Differential Equations are featured. The expert examines the first-order differential equations. Explanations. ...

... Rewriting: (1.33) This is a Bernoulli with n=3, so we set: (1.34) Thus ... The first order differential equations, partial DE's and linear functions are provided. ...

... The solution is comprised of detailed explanations on how to set up the first order differential equation when there are two tanks connected together and ...

... to the attached Word document for the complete solutions to the problem set. ... as an equivalent problem for a system of first-order differential equations. ...

... form of writing a system of differential equations is ... some arbitrary constant and this will set the value ... like to write it as a system of first order equations. ...

...Equation (1.8) becomes: (1.11) So if we equate coefficients on both sides we get a set of n first order ordinary differential equations for : (1.12) Since this ...

... Modelling the second order differentail equation describing the ... point in time we use the first differential with respect ... This can be found by setting dx / dt ...