Please answer the following question clearly and show your work. Exercise 17.30

Question

Please answer the following question clearly and show your work.

Exercise 17.30 Part A A 30000 kg subway train initially traveling at 20.0 m/s slows to a stop in a station and then stays there long enough for its brakes to cool. The station's dimensions are 65.0 m long by 20.0m wide by 12.0 m high Assuming all the work done by the brakes in stopping the train is transferred as heat uniformly to all the air in the station, by how much does the air temperature in No Cre to be 1.20 kg/m and its specific heat to be 1020 J/kg-K) Submit My Answers Give up

Explanation / Answer

17.3) kinetic energy = heat energy
(1/2) (mass)(velocity)^2 = (mass)(specific heat)(change in temperature)
(1/2)m(v^2) = m(Cp)(dT)

from density = mass over volume,
mass(m) = density(D) times volume(V)

(1/2)m(v^2) = DV(Cp)(dT)
(1/2)(30000kg)(20 m/s)^2 = (1.2 kg/m3)(65m x 20m x12m)(1020J/kg-K)(dT)
solve for (dT),
dT = 0.314 Kelvin or 0.314 degree C

17.4) heat of fusion ice = 334*10^3 J/kg
c of ice= 2100 J/kgK
c of water = 4190 J/kgK

Now Q = mi.ci.T - mi.L
Q1 = mw.cw.T1
Q+Q1 = (mi + mw).cw.Tf
mw = mi.(cw.Tf - ci.T + L)/(cw.(T1-Tf))
mw = 0.19*(4190*28 + 2100*36 + 334000)/(4190*(80-28)) = 0.46 kg

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