A substan e has a melting point of 20◦C and a heat of fusion of 3.5 × 104 J/kg. The boiling point is 150◦C and the heat of vaporization is 7.0 × 104 J/kg at a pressure of 1.0 atm. The spe i heats for the solid, liquid, and gaseous phases are 600 J/(kg. K), 1000 J/(kg. K), and 400 J/(kg. K), respe tively. The quantity of heat given up by 0.50 kg of the substan e when it is ooled from 170◦C to 88◦C, at a pressure of 1.0 atmosphere, is losest to (1) 70 kJ (2) 14 kJ (3) 21 kJ (4) 30 kJ (5) None of the above.

Option (1) 70 kJ

Explanation:

Given that;

melting point of the substance T₁ is 20°C , Boiling point of the substance T₂ is 150°C , heat of fusion L₁ is 3.5 x 10⁴ J/kg , heat of vaporization L₂ is 7 x 10⁴ J/kg , Specific heat in solid state C₁ is 600 J/kg.K , Specific heat in liquid state C₂ is 1000 J/kg.K, Specific heat in gaseous state C₃ is 400 J/(kg.K) , Mass of the substance m is 0.5 kg , Initial temperature of the substance T₃ is 170°C , Final temperature of the substance  T₄ is 88°C .

Now  Heat given up by the substance to reach boiling point 150°C is

Q₁ = mC₃(T₃ - T₂)

Q₁ = (0.5)(400)(170 - 150)

Q₁ = 4000 J

Heat given up by the substance to turn into liquid from gaseous state at 150°C

Q₂ = mL₂

Q₂ = (0.5)(7x10⁴)

Q₂ = 35000 J

Heat given up by the substance to reach 88°C in liquid state from 150°C

Q₃ = mC₂(T₂ - T₄)

Q₃ = (0.5)(1000)(150 - 88)

Q₃ = 31000 J

Total heat given up by the substance

Q = Q₁ + Q₂ + Q₃

Q = 4000 + 35000 + 31000

Q = 70000 J

Q = 70 kJ

Therefore The quantity of heat given up by 0.50 kg of the substance when it is cooled from 170◦C to 88◦C, at a pressure of 1.0 atmosphere, is closest to 70 kJ

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.

i believe the answer would be:

d. violin, clarinet, french horn, and tuba