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6. Sand is pouring from a funnel onto a cone-shaped pile which is 20 feet high and 50 feet in diameter at its base. If the sand is coming out of the funnel at a rate of 2.5 cubic feet per second, how long will it take for the height of the pile to increase 1 inch, assuming that the shape of the pile does not change?

Sagot :

To determine how long it will take for the height of the cone-shaped sand pile to increase by 1 inch, we need to go through the following steps:

1. Understand the Given Data:
- Initial height of the cone, [tex]\( h_{initial} = 20 \)[/tex] feet.
- Diameter of the base of the cone, [tex]\( d = 50 \)[/tex] feet. Therefore, the radius [tex]\( r = \frac{d}{2} = 25 \)[/tex] feet.
- Volume flow rate of sand from the funnel, [tex]\( Q = 2.5 \)[/tex] cubic feet per second.
- Increase in height, [tex]\( \Delta h = \frac{1}{12} \)[/tex] feet (since 1 inch is [tex]\(\frac{1}{12}\)[/tex] of a foot).

2. Calculate the Initial Volume of the Cone:
To find the initial volume of the cone-shaped pile, we use the formula for the volume [tex]\( V \)[/tex] of a cone:

[tex]\[ V_{initial} = \frac{1}{3} \pi r^2 h_{initial} \][/tex]

Substituting the values:

[tex]\[ V_{initial} = \frac{1}{3} \pi (25^2) (20) \][/tex]

Calculating it gives:

[tex]\[ V_{initial} \approx 13089.97 \text{ cubic feet} \][/tex]

3. Calculate the Final Volume of the Cone:
The final height of the cone after the increase by 1 inch is:

[tex]\[ h_{final} = h_{initial} + \Delta h = 20 + \frac{1}{12} \][/tex]

Now, calculate the final volume [tex]\( V_{final} \)[/tex]:

[tex]\[ V_{final} = \frac{1}{3} \pi r^2 h_{final} \][/tex]

By substituting the values, we get:

[tex]\[ V_{final} = \frac{1}{3} \pi (25^2) \left( 20 + \frac{1}{12} \right) \][/tex]

Calculating it gives:

[tex]\[ V_{final} \approx 13144.51 \text{ cubic feet} \][/tex]

4. Determine the Volume of Sand Added:
The volume of sand added to increase the height by 1 inch is the difference between the final volume and the initial volume:

[tex]\[ V_{added} = V_{final} - V_{initial} \][/tex]

[tex]\[ V_{added} \approx 13144.51 - 13089.97 = 54.54 \text{ cubic feet} \][/tex]

5. Calculate the Time Required:
To find the time [tex]\( T \)[/tex] required to add this volume of sand at the given rate, we use the formula:

[tex]\[ T = \frac{V_{added}}{Q} \][/tex]

Substituting the values:

[tex]\[ T = \frac{54.54}{2.5} \][/tex]

Thus, the time required is:

[tex]\[ T \approx 21.82 \text{ seconds} \][/tex]

Hence, it will take approximately 21.82 seconds for the height of the sand pile to increase by 1 inch.