1.The pressure in the atmosphere is not constant, but fluctuates as the weather
ID: 1306527 • Letter: 1
Question
1.The pressure in the atmosphere is not constant, but fluctuates as the weather changes. If the pressure outside a window drops by 4% while the pressure inside does not change, what is the force on the window? Assume the area of the window is 1.9 m2.(The positive direction is toward the inside of the window. Indicate the direction with the sign of your answer. Assume that the initial pressure inside and outside the window is initially 1 atm.)
Previous incorrect answers given: 1.82e5N, 7.70e3N
2.Consider a rectangular swimming pool of depth 1.9 m with a width and length of 13 m. What is the force exerted by the water on one of the sidewalls of the pool?
previous answers given: 2.30e5 N , 1.57e6 N
a.Find h. (Assume h is positive.)
P1-P2= ?
Previous answers given: .0954 Pa, 12.3 Pa
Explanation / Answer
1)
let P = atmospheric pressure in Pascals
Force = Press Difference x Area
Force = 0.04P(1.9) = 0.076P = __________ N ANS {U can do this now :>)
2)
Alright, as the conditions were not given, I'll assume it is at SATP (25C and 100KPa). First off, the formula for hydrostatic pressure, the pressure of a standing, contained liquid, is P = pgh + Pa Where P is the hydrostatic pressure in Pascals, p is the density of the liquid (assuming pure water at SATP it is 997 Kg/m^3), g is the acceleration (in this case due to gravity which is 9.8 m/s^2), h is the height or depth of the water (1.9m), and Pa is the atmospheric pressure (in this case 100KPa, or 100000 Pa). So, plugging that in, there is a pressure of 118564.14 Pa. As this unit means 1N/m^2, and the surface area is 13mX13m, i.e. 169m^2, then the total force exerted on the bottom of the pool due to the water pressure is 2.003 X 10^7 N.
Edit: Yes, SATP stands for Standard Atmospheric Temperature and Pressure. This is one of two conditions defined by the International Union of Pure and Applied Chemistry, the other being Standard Temperature and Pressure. SATP is 25C, and 100kPa. STP is defined as 0C (or 273K) and 100kPa. SATP is more useful here because it has water in its liquid state. Do not get confused when people say that the pressure is 1 atm, because that is 101.325 kPa, and not the official definition.
3)
On one side you have a column of blue fluid of known density and height, so you can calculate the weight. On the other side you have a column of red fluid of known density and height (20 - h) plus a 20g weight, so you can calculate the total weight. The weights on the left and right sides are equal, so you can solve the equation for h
4)
cross section area of pipe (A)= 3.14*r^2= 3.14*(.0022m)^2 =0.0000151976 m^2
velocity= (1.8* 10-7)/0.0000151976=0.01184 m/s
p1-p2 = (8*0.0027*0.18m*0.01184 m/s) /0.00000484 = 9.5114 Pascal = ur final answer
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