a 34 34gm cube of ice Please help urgent 18. A very loud train whistle has an ac

Question

a 34 34gm cube of ice

Please help urgent

18. A very loud train whistle has an acoustic power output of 90 watts. If the sound energy spreads out spherically. what is the intensity level in dB at a distance of 1 1 5 meters from the train? (Io = 10-12 Watts/m 2) A) 108 dB B) 51.84 dB (C) 87.34 dB D) 194.58 dB E) 86.4 dB 19. A mass on a spring vibrates in simple harmonic motion at a frequency of 6 Hz and an amplitude of 7 cm. If a timer is started when its acement is a maximum (hence x = 7 cm when t-0), what is the displacement of the mass when t = 2.4 s? A) +5.663 cm B) -17.5 cm C) 12.6 cm D) 4 cm E) 4.32cm ped fans 20m or wa m25 Wat er in a 110 gm aluminum container, both initilly at 25° C. What 20. A 34 gm cube of ice nr is the final equilibrium temperature? (Specific heat for aluminum is 0.215 cal/gm-Co and Ls 80 cal/gm.) A) 13.84 °C B) 5.3856 °C C) 11.333333 oC D) 24°C E) 14.45 °C Version 2 Page 2

Explanation / Answer

20. as ice melts, energy absorbed by it
  
Q1 = m Lf = 34 x 80 = 2720 cal

energy absorbed as temp increases to final temp(say T)

Q2 = m C deltaT = 34 x 1 x (T - 0) = 34 T

energy released by water and aluminium as temp drops.

Q3 = (220 x 1 x (25 - T)) + (110 x 0.215 x (25 - T))

Q3 = 5500 - 220T + 591.25 - 23.65T

Applying energy conservation(assuming no heat/energy loss)

Q1 + Q2 = Q3

2720 + 34T = 6091.25 - 243.65T

T = 12.14 deg C

there is no such option.

If you have to choose any of these,

then Option C is best option.

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