# Kinetic energy, Potential energy and change in water pressure

• Northbysouth
In summary, the conversation discusses the calculation of kinetic energy, potential energy, and pressure difference in various scenarios. The equations for calculating these values are provided and applied to specific examples. Additional guidance is given for finding the density of water in order to calculate pressure difference.
Northbysouth

## Homework Statement

I'm not particularly confident with my calculations and I would appreciate any feed back.

A) What is the kinetic energy of an object with:
mass = 5lbm
velocity = 200 ft/sec

B) What is the potential energy of an object with:
mass = 5lbm
height = 200ft
g = 32.2 ft/sec2

C) What is the pressure difference between the top and bottom of a water column that is 15ft high and gravity is 32.2 ft/sec2

KE = 1/2mv2/gc

PE = mgh/gc

## The Attempt at a Solution

A)
KE = 1/2(5 lbm)(200 ft/sec)2/32.17 ft-lbm/lbf-sec2
KE = 3.11x103 lbf-ft

B)
PE = (5 lbm)(32.2 ft/sec2)(200ft)/32.17 ft-lbm/lbf-sec2
PE = 1001 lbf-ft

C) I'm not quite sure where to start with this one and I would appreciate an guidance.

Hi Northbysouth!
Northbysouth said:
A)
KE = 1/2(5 lbm)(200 ft/sec)2/32.17 ft-lbm/lbf-sec2
KE = 3.11x103 lbf-ft

B)
PE = (5 lbm)(32.2 ft/sec2)(200ft)/32.17 ft-lbm/lbf-sec2
PE = 1001 lbf-ft

yes, they look fine to me, except:

i] i don't understand the pound system , so i can;t confirm whether you need to divide by g !
ii] if the question asks you to take g as 32.2, then shouldn't you use the same figure instead of 32.17 ?
C) I'm not quite sure where to start with this one and I would appreciate an guidance.

you'll need to find the density of water (mass per cubic foot) …

pressure = weight/area = density*height*area/area = density*height

tiny-tim said:
Hi Northbysouth!

yes, they look fine to me, except:

i don't understand the pound system , so i can;t confirm whether you need to divide by g !
Since the problem says that the mass (rather than weight) is "5 lbm", no, you shouldn't divide by g. "1 lbm" or "one pound mass" is the mass of an object that has, in standard gravity, a weight of 1 lb. The division by g has already been done.

[ii] if the if the question asks you to take g as 32.2, then shouldn't you use the same figure instead of 32.17 ?

you'll need to find the density of water (mass per cubic foot) …

pressure = weight/area = density*height*area/area = density*height

## 1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is dependent on the mass and velocity of the object.

## 2. What is potential energy?

Potential energy is the energy an object possesses due to its position or state. It can be stored in various forms such as gravitational, elastic, or chemical potential energy.

## 3. How is kinetic energy related to potential energy?

Kinetic energy and potential energy are two forms of energy that can be converted into each other. When an object moves from a higher potential energy state to a lower one, the potential energy is converted into kinetic energy.

## 4. How does water pressure change with depth?

Water pressure increases with depth due to the weight of the water above. The deeper the water, the greater the pressure exerted by the water above.

## 5. How does the change in water pressure affect kinetic and potential energy?

As water pressure increases with depth, the potential energy of the water also increases due to the increased weight above. This means that more potential energy is available to be converted into kinetic energy when the water starts to move. Additionally, the kinetic energy of the moving water can also contribute to changes in water pressure, such as waves or currents.

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