A swimming pool is 20 ft wide, 40 ft long, 3 ft deep at the shallow end, and 9 feet deep at its deepest point. If the pool is being filled at a rate of 0.8ft3/min, how fast is the water level rising when the depth at the deepest point is 5 ft

Respuesta :

Using implicit differentiation, it is found that the water level is rising a rate of 0.001 ft/sec.

The volume of a pool of length l, width w and height h is given by:

[tex]V = lwh[/tex]

Applying implicit differentiation, the rate of change of the volume is given by:

[tex]\frac{dV}{dt} = wh\frac{dl}{dt} + lh\frac{dw}{dt} + lw\frac{dh}{dt}[/tex]

Neither the width nor the length changes, hence [tex]\frac{dl}{dt} = \frac{dw}{dt} = 0[/tex], and:

[tex]\frac{dV}{dt} = lw\frac{dh}{dt}[/tex]

We are given that:

[tex]\frac{dV}{dt} = 0.3, l = 20, w = 40[/tex], hence:

[tex]\frac{dV}{dt} = lw\frac{dh}{dt}[/tex]

[tex]0.8 = 20(40)\frac{dh}{dt}[/tex]

[tex]\frac{dh}{dt} = \frac{0.8}{800}[/tex]

[tex]\frac{dh}{dt} = 0.001 [/tex]

Water level is rising at rate of 0.001 ft/sec.

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