Question
What is the entropy change to turn 12 grams of ice (C_ice = 53 cal/gr degree C) at -30 degree to 10 grams of steam? A) 45 cal./K B) 31.68 cal./K C) 10.56 cal./K D) 19.9 cal./K E) 61.2 cal./K A gasoline engine with an efficiency of 30% operates between a high temperature T_1 and a low temperature T_2 = 25 degree C. If this engine operates with Carnot efficiency, what is the high-side temperature T_1? A) 28.2 degree C B) 332.25 degree C C) 84.6 degree C D) 798 degree C E). 152.7 degree C y = 6 sin(2 t - 5 x). Velocity of propagation of the wave is A) 1.2 B) 2 C) 2.4 D) 0.4 E) 2.5 Diatomic hydrogen explodes adiabatically to 34 times its original volume before its pressure reduces back to atmospheric pressure. When ignited, what was its initial pressure? A) 79.3 Atm B) 102.34 Atm C) 139.3 Atm D) 10.2 Atm E) 306 Atmmiddot The tungsten filament of a lightbulb has an operating temperature of about 2700 degree C when the room temperature is 20 degree C. If the emitting area of the filament is 1.1 cm^2, and its emissivity is 0.6, what is the power output of the lightbulb? (Stephan-Boltzmann Constant = 5.67 times 10^-8 W/m^2 K^4) A) 16.2 Watts B) 276.21 Watts C) 37.26 Watts D) 49.5 Watts E) 29.23 Watts What is the entropy change for 7 moles of a polyatomic ideal gas isobaric process from 23 degree C to 100 degree C? A) 53.83 J/K B) 19.3 J/K C) 161 J/K D) 48.3 J/K E) 70 J/K A 300 Hz siren is moving at 90 f/s toward a person running away from it at 20 f/s. What pitch does the person hear? (V_sound = 1100 f/s) A) 120 Hz B) 320.8 Hz C) 135 Hz D) 1080 Hz E) 60 Hz A 3 loop string has a linear mass density of 28 grams/cm and a length of 70 cm. If the tension in the string is 19 N, at what frequency is the string vibrating? A) 55.82 Hz B) 57 Hz C) 11.1 Hz D) 69.3 Hz E) 171 Hz If the distance between a point sound source and a dB detector is increased by a factor of 8, what will be the reduction in intensity level? A) 28.872N B) 10.9N C) 21.12 N D) 7.04 N E) 18.06 N The density of a certain metal solid is 7.8 times I0^3 kg/m^3 and its Young's modulus is 1.5 times 10^11 N/m^2. What is the velocity of sound in this metal? A) 1300 m/s B) 7371 m/s C) 3744 m/s D) 4385 m/s E) 11934 m/s
Explanation / Answer
Solving first question
Heat required=12*30*0.53 +12*1*100 +12*80.3 +10*540
entropy change=Heat/temperature
temperature=-30+273=243 K
Entropy change=31.9 cal/k
option (b) is correct
Question 2
Efficiency=(Th-Tc)/Th
Tc=25+273=298 K
0.3=(Th-298)/Th
we got Th=425.7 K=152.7 C
option (E) is correct
