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Force needed to pull out a plug out of a drain under water?

  • #1

Homework Statement


The plug for the drain of a water tower is located 3.0 m below the surface. The plug is circular and has a diameter of 5.0 cm. If the density of water is 1000 kg/m3 , how much force is required to remove the plug (you may ignore the weight of the plug itself)

Homework Equations


A= pi * r ^2
F=P *A

The Attempt at a Solution


A = pi * r^2 = pi * (0.025)^2 =1.96 * 10 ^-3 m^2

F= pGH * A
= (1000 kg/m3) (9.8) (3.0 m) * 1.96 * 10 ^-3 m^2
= 57.624 N

is this correct? there is no pressure from the atmosphere right?
 

Answers and Replies

  • #2
19,915
4,092

Homework Statement


The plug for the drain of a water tower is located 3.0 m below the surface. The plug is circular and has a diameter of 5.0 cm. If the density of water is 1000 kg/m3 , how much force is required to remove the plug (you may ignore the weight of the plug itself)

Homework Equations


A= pi * r ^2
F=P *A

The Attempt at a Solution


A = pi * r^2 = pi * (0.025)^2 =1.96 * 10 ^-3 m^2

F= pGH * A
= (1000 kg/m3) (9.8) (3.0 m) * 1.96 * 10 ^-3 m^2
= 57.624 N

is this correct? there is no pressure from the atmosphere right?
The atmospheric pressure is in addition to the 58N to give the total pressure from above. The pressure from below is just atmospheric. So the atmospheric pressure cancels.
 

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