ANSWERS:

**1.** Into a 100-gal tank initially filled with freshwater flow 3 gal/min of salt water containing 2 pounds of salt per gallon. The solution kept uniform by stirring, flows out at the same rate. What is the upper limit for the number of pounds of salt in the tank if the process continues indefinitely?

**A. 200 lb **

**2. **From the data in the previous problem, how much time will elapse while quantity of salt in the tank changes from 100 to 150 lb?

**C. 23.1 min**

**3.** A mothball loses mass by evaporation at a rate that is proportional to the surface area. If half the mass is lost in 100 days, how long will it take the radius to decrease to half its initial value?

**A. 243 days **

**4. **Assume that the rate of change of air pressure with altitude is proportional to the air pressure. If the air pressure on the ground is 14.7 psi and if at an altitude of 10,000 ft it is 10.1 psi. Find the air pressure at an altitude of 15,000 ft.

**D. 8.37 psi**

**5. **A 50-kg steel pipe 4.0 m long is supported by a rope attached 1.7 m from one end. The downward force that must be applied to the end of the pipe closest to the rope to keep the pipe horizontal is

**B. 86 N**

**IMPORTANT NOTE: **These are just practice problems I randomly collected solely for review purposes only. This should not be substituted to textbooks. Please read and study your textbooks well.

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