Chapter 7, Problem 68RE

If a coffee filter is dropped, its velocity after t seconds is given by v(t)=4(10.0003t) feet per second. What is the terminal velocity, and how long does it take the filter to reach 99 of terminal velocity? Use a table increment of 0.1 and given your answer to the nearest tenth of a second.

The amount of electrical resisitance (R) in a medium depends on the temperature, and for certain materials can be modeled by the equation R(t)+0.01t^2+0.1t+k, where R(t) is the resistance in ohms at temperature t(t>or equal to 0degrees) in degrees Celsius, and k is the resistance at t=0degreesC Suppose k=30 for a certain medium. Write the resistances equation and use it to answer the following.  a. For what temperature is the resistance less than 42 ohms b. For what temperature is the resistance greater than 42 ohms c. If it becomes uneconomical to run electricity through the medium for resistance greater than 60 ohms for what temperatures should the electricity generator be shut down?

A tank contains 1000-gallon of pure water. Starting at time t = 0, a solution containing 0.2 lb of salt per gallon enters 10 gallons per minute and the well-stirred solution is withdrawn at a rate of 5 gallons per minute. Set up the initial value problem for the amount of salt, Q(t), in the tank as a function of t. Sove for Q(t).