Submitted by: Submitted by massa005
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Pages: 2
Category: Science and Technology
Date Submitted: 02/02/2016 07:25 AM
Exponential Growth and Decay Answers:
1. A bacteria culture initially contains 120 cells and grows at a rate proportional to its size. After
one hour the population has increased to 200 cells.
.
a. Find an expression for the number of bacteria after hours.
=
b. Find the rate of growth after 2 hours. 170 bacteria per hour
c. When will the population reach 5000 cells? After 7.3 hours
2. Cesium-137 has a half-life of 30 years. Suppose you have a 40mg sample.
.
a. Find the mass that remains after years.
=
b. How much of the sample remains after 10 years? 31.7mg
c. What percentage of the sample remains after 10 years? 79.4%
d. After how long will only 2mg remain? About 130 years
3. When a cold drink is taken from a refrigerator, it temperature is 6°C. After 30 minutes in a 22°C
room, the temperature of the drink has increased to 11°C.
a. What is the temperature of the drink after one hour? 14.4°C
b. When will the temperature of the drink reach 19°C? After 134 minutes or 2.23 hours
4. It is known that carbon-14 has a half-life of about 5730 years. Suppose that charcoal found in an
archeological dig contain about 62% carbon-14 radioactivity as plant material on the earth
today. Estimate the age of the charcoal. About 3950 years old
5. A curve passes through the point (0,4) and has the property that the slope of the curve at every
point is twice the y-coordinate of . What is the equation of the curve? =
6. A body is found at a crime scene. At 2:00pm the temperature of the body is 32.6°C and at
3:00pm the temperature has decreased to 30.4°C. Normal body temperature is about 37.0°C
and the temperature of the surroundings is 20.0°C. Estimate the time of death. About 12:26pm