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Consider a tank used in certain hydrodynamic experiments. After one experiment the tank contains 200 liters of a dye solution with a concentration of 1 g/liter. To prepare for the next experiment, the tank is to be rinsed with fresh water flowing in at a rate of 2 liters/min, the well-stirred solution flowing out at the same rate.Find the time that will elapse before the concentration of dye in the tank reaches 1% of its original value.

Solution

Let Q(t) represent the amount of dye at any time t. Q' represent the net rate of change of amount of dye in the tank. Q' = inflow - outflow.

inflow = 0 (since the incoming water contains no dye)

outflow = concentration × rate of water inflow

Concentration = Quantity/volume = Q/200

outflow = concentration × rate of water inflow = Q/200 g/liter × 2 liters/min = Q/100 g/min.

So, Q' = inflow - outflow = 0 - Q/100

Q' = -Q/100 This is our differential equation. We solve it as follows

Q'/Q = -1/100

∫Q'/Q = ∫-1/100

㏑Q = -t/100 + c

$Q(t) = e^{(-t/100 + c)} = e^{(-t/100)}e^{c} = Ae^{(-t/100)}\\Q(t) = Ae^{(-t/100)}$

when t = 0, Q = 200 L × 1 g/L = 200 g

$Q(0) = 200 = Ae^{(-0/100)} = Ae^{(0)} = A\\A = 200.\\So, Q(t) = 200e^{(-t/100)}$

We are to find t when Q = 1% of its original value. 1% of 200 g = 0.01 × 200 = 2

$2 = 200e^{(-t/100)}\\\frac{2}{200} = e^{(-t/100)}$

㏑0.01 = -t/100

t = -100㏑0.01

t = 460.52 min

6 0

2 years ago

A team t-shirt costs $3 per adult and $2 per child. On a certain day, the total number of adults (a) and children (c) who bought

lesya [120]

A+c=100

3a+2c=275, from the first c=100-a making the 2nd equation become:

3a+2(100-a)=275 perform indicated multiplication on left side

3a+200-2a=275 combine like terms on left side

a+200=275, subtract 200 from both sides

a=75, and since c=100-a

c=100=75=25

So the answer is D. 25 children and 75 adults
Equation 1: a+c=100
Equation 2: 3a+2c=275

8 0

2 years ago

The 200 meter race times at a state track meet are normally distributed with a mean of 13.56 seconds and a standard deviation of

BaLLatris [955]

Answer:

A. 0.4880

Step-by-step explanation:

First, find the z-score:

z = (x − μ) / σ

z = (13.5 − 13.56) / 2.24

z = -0.03

Using a z-score table:

P(z < -0.03) = 0.4880

8 0

2 years ago

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