A2.4-m-high 200-m2 house is maintained at 22°c by an air-conditioning system whose cop is 3.2. it is estimated that the kitchen, bath, and other ventilating fans of the house discharge a houseful of conditioned air once every hour. if the average outdoor temperature is 32°c, the density of air is 1.20 kg/m3, and the unit cost of electricity is $0.1/kwh, the amount of money "vented out" by the fans in 10 hours is consider the specific heat to be 1.005 kj/kg·°c.

Cost= 0.5 $

Explanation:

Coefficient of performance of the air conditioning system is given as

Energy = energy discharged or vented every hour= m c ΔT

Q = heat energy (Joules, J)

m = mass of a substance (kg)

c = specific heat (units J/kg∙K)

∆ is a symbol meaning "the change in"

∆T = change in temperature (Kelvins, K)

therefore

where m = ρV = density of air x volume = 1.20 x 200 x 2.4 = 576Kg

Energy = energy discharged or vented every hour=  ρVc ΔT

Q= 576 x 1.005 x 10 = 5760 KJ/hour

therefore=ore 1kw = 3600KJ/hour

Q = 1.6 Kwh

Q =

Cost = per unit cost x energy vent x no of hours

Cost = 0.1 x 0.5 x 10

Cost= 0.5 $

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form