Question

A huge tank of glycerine with a density of 1.260 g/cm3 is vertically stationed on a platform which is 15 m above the ground. The glycerine level is 5 m above the base of the tank. A small hole 4 mm in diameter has formed in the base of the tank. Both the hole and the top of the tank are open to the air.

A) How many cubic meters of glycerine per second is this tank losing? (hint: the speed of the flow at the top of the tank is pretty small and negligible
B) How fast is the water from the hole moving just as it reaches the ground?

Answer 1

The tank is losing
`4.976*10^(-4) m^3/s`

`v_g = 19.81 \ m/s`

Step-by-step explanation:

According to the Bernoulli’s equation:

`P_1 + 1 (1)/(2) \rho v_1^2 + \rho gh_1 = P_2 + (1)/(2) \rho v_2^2 + \rho gh_2`

We are being informed that both the tank and the hole is being exposed to air :

∴ P₁ = P₂

Also as the tank is voluminous ; we take the initial volume
`v_1` ≅ 0 ;

then
`v_2` can be determined as:
`\sqrt{[2g (h_1- h_2)]`

h₁ = 5 + 15 = 20 m;

h₂ = 15 m

`v_2 = \sqrt{[2*9.81*(20 - 15)]`

`v_2 = \sqrt{[2*9.81*(5)]`

`v_2= 9.9 \ m/s` as it leaves the hole at the base.

radius r = d/2 = 4/2 = 2.0 mm

(a) From the law of continuity; its equation can be expressed as:

J =
`A_1v_2`

J = πr²
`v_2`

J =
`\pi *(2*10^(-3))^(2)*9.9`

J =
`1.244*10^(-4) m^3/s`

b)

How fast is the water from the hole moving just as it reaches the ground?

In order to determine that; we use the relation of the velocity from the equation of motion which says:

v² = u² + 2gh ₂

v² = 9.9² + 2×9.81×15

v² = 392.31

The velocity of how fast the water from the hole is moving just as it reaches the ground is :
`v_g = √(392.31)`

`v_g = 19.81 \ m/s`