QUESTION IMAGE
Question
- without changing the volume of the can, come up with two new can designs—a taller can and a wider can—and record their dimensions below.
table with columns: height, radius, volume. original: height 12.1 cm, radius 3.1 cm, volume 365.31 cm³. other columns have partial writing (e.g., 2.5 cm radius?)
- a colleague argues that doubling the radius of the can and halving the height will keep the volume the same. is this true? why or why not?
- meijer sells bubly water and is offering a president’s day sale on its individual cans. for the price of an original size can of bubly you can choose either:
a. a can with the same height but twice the radius or
b. a can with the same radius but twice the height
which offer is the better deal? explain.
- suppose you had the option of buying a can with twice the radius and twice the height for triple the price. is this a better or worse deal than either of the two options above? explain.
Question 2 Solution:
First, recall the volume formula for a cylinder: \( V=\pi r^{2}h \). The original volume is \( V = \pi\times(3.1)^{2}\times12.1\approx365.31\space cm^{3}\).
Taller Can (Decrease Radius, Increase Height):
Let's choose a new radius, say \( r = 2.5\space cm \). We need to find \( h \) such that \( \pi r^{2}h=365.31 \).
Step 1: Rearrange the volume formula for \( h \)
\( h=\frac{V}{\pi r^{2}} \)
Step 2: Substitute \( V = 365.31 \) and \( r = 2.5 \)
\( h=\frac{365.31}{\pi\times(2.5)^{2}}\approx\frac{365.31}{19.635}\approx18.6\space cm \)
Wider Can (Increase Radius, Decrease Height):
Let's choose a new radius, say \( r = 4\space cm \). We need to find \( h \) such that \( \pi r^{2}h = 365.31 \).
Step 1: Rearrange the volume formula for \( h \)
\( h=\frac{V}{\pi r^{2}} \)
Step 2: Substitute \( V = 365.31 \) and \( r = 4 \)
\( h=\frac{365.31}{\pi\times(4)^{2}}\approx\frac{365.31}{50.265}\approx7.27\space cm \)
Filling the table:
| Height | 12.1 cm | 18.6 cm | 7.27 cm |
|---|---|---|---|
| Volume | \( 365.31\space cm^{3} \) | \( 365.31\space cm^{3} \) | \( 365.31\space cm^{3} \) |
Question 3 Solution:
The volume of a cylinder is given by \( V=\pi r^{2}h \). Let the original radius be \( r \) and original height be \( h \), so original volume \( V_{1}=\pi r^{2}h \).
If we double the radius (\( r_{2} = 2r \)) and halve the height (\( h_{2}=\frac{h}{2} \)), the new volume \( V_{2}=\pi(2r)^{2}\times\frac{h}{2} \).
Step 1: Simplify \( V_{2} \)
\( V_{2}=\pi\times4r^{2}\times\frac{h}{2}=2\pi r^{2}h \)
Step 2: Compare \( V_{1} \) and \( V_{2} \)
We can see that \( V_{2} = 2V_{1} \), which means the volume doubles, not stays the same. So the colleague's argument is false because doubling the radius (which is squared in the volume formula) has a larger impact than halving the height.
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(Question 3):
No, it is not true. When the radius is doubled (\( r
ightarrow2r \)) and height is halved (\( h
ightarrow\frac{h}{2} \)), the new volume \( V_{new}=\pi(2r)^{2}(\frac{h}{2}) = 2\pi r^{2}h=2V_{original} \), so the volume doubles, not remains the same.
Question 4 Solution:
Let the original radius be \( r \) and original height be \( h \), so original volume \( V=\pi r^{2}h \).
Option a: Same height, twice the radius (\( r_{a}=2r \), \( h_{a}=h \))
Volume of option a: \( V_{a}=\pi(2r)^{2}h=\pi\times4r^{2}h = 4\pi r^{2}h=4V \)
Option b: Same radius, twice the height (\( r_{b}=r \), \( h_{b}=2h \))
Volume of option b: \( V_{b}=\pi r^{2}(2h)=2\pi r^{2}h = 2V \)
Since \( V_{a}=4V \) and \( V_{b}=2V \), and both cost the same as the original can (which has volume \( V \)), option a gives a larger volume (4 times the original) compared to option b (2 times the original). So option a is a better deal.