Th e heat capacity of air is much smaller than that of water, and relatively modest amounts of heat are needed to change its temperature. th is is one of the reasons why desert regions, although very hot during the day, are bitterly cold at night. th e heat capacity of air at room temperature and pressure is approximately 21 j k−1 mol−1. how much energy is required to raise the temperature of a room of dimensions 5.5 m × 6.5 m × 3.0 m by 10°c? if losses are neglected, how long will it take a heater rated at 1.5 kw to achieve that increase given that 1 w = 1 j s−1?

Q=1005 J

t= 0.67 sec

Explanation:

Lets take condition of room is 1 atm and 25°C.

Heat capacity ,c = 21 J /K.mol

If we assume that air is ideal gas that

P V = n R T

V= 107250 L

At STP number of moles given as

V=22.4 L at S.T.P.

n=4787.94 moles

n= 4.784 Kmoles

So heat required to raise 10°C temperature

Q = n x c x ΔT

Q = 4.78794 x 21 x 10

Q=1004.64 J

Time t

t= Q/P

P= 1.5 KW

t = 1.004.64 /1.5

t= 0.66 sec

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

helium

oxygen

neon

sodium