A bucket full of water is in the form of a frustum. The bottom and top radii of the frustum are 18 cm and 28 cm respectively, and the vertical depth is 30 cm. If the water in the bucket is poured into an empty cylindrical container with a radius of 20 cm, find the depth of the water in the container.



Answer :

Sure, let’s go step by step to solve the given problem.

Given:
- The bucket is in the shape of a frustum.
- The bottom radius of the frustum [tex]\( r_1 = 18 \)[/tex] cm.
- The top radius of the frustum [tex]\( r_2 = 28 \)[/tex] cm.
- The height of the frustum [tex]\( h_f = 30 \)[/tex] cm.

We need to find the volume of the frustum first. The formula for the volume [tex]\( V \)[/tex] of a frustum is:

[tex]\[ V_{\text{frustum}} = \frac{1}{3} \pi h \left( R^2 + r^2 + Rr \right) \][/tex]

Substituting the given values:
[tex]\[ R = 28 \text{ cm} \][/tex]
[tex]\[ r = 18 \text{ cm} \][/tex]
[tex]\[ h = 30 \text{ cm} \][/tex]

[tex]\[ V_{\text{frustum}} = \frac{1}{3} \pi \times 30 \left( 28^2 + 18^2 + 28 \times 18 \right) \][/tex]

After calculating this expression, we get:
[tex]\[ V_{\text{frustum}} \approx 50642.47 \text{ cm}^3 \][/tex]

Next, we need to determine the height of water when the frustum-shaped water is poured into a cylindrical container with radius [tex]\( r_{\text{cylinder}} = 20 \text{ cm} \)[/tex].

The volume of a cylinder [tex]\( V \)[/tex] is calculated using the formula:

[tex]\[ V_{\text{cylinder}} = \pi r^2 h \][/tex]

Here, we need to solve for height [tex]\( h \)[/tex] given:
[tex]\[ V_{\text{cylinder}} = V_{\text{frustum}} \][/tex]

So,
[tex]\[ V_{\text{cylinder}} = \pi \times 20^2 \times h \][/tex]

Since the volume of the cylinder must equal the volume of the frustum:
[tex]\[ 50642.47 = \pi \times 400 \times h \][/tex]

Dividing both sides by [tex]\( \pi \times 400 \)[/tex], we get the height [tex]\( h \)[/tex] of the water in the cylinder:

[tex]\[ h = \frac{50642.47}{\pi \times 400} \][/tex]
[tex]\[ h \approx 40.30 \text{ cm} \][/tex]

So, the depth of the water in the cylindrical container is approximately 40.30 cm.