Physics—Fluids, Waves, Thermodynamics, and Optics Answers 7) E 8) E 9) C 10) C I
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Physics—Fluids, Waves, Thermodynamics, and Optics Answers
7) E 8) E 9) C 10) C
I've given the answers above, if you can please explain the answers and how to get it I will greatly appreciate it.
7. Asphalt has a specific heat of around 900J/kg/K and a density of 2000 kg/m". Consider a UCSD park- ing lot (made of asphalt) that is square, 200 m on a side, and .25m thick. Sunlight of intensity 1kW/m' is incident on the parking and heats it up during our "winter" months. How long does it take to heat the parking lot up from its temperature during the night, around 0 C, to its daytime temperature, around 30 C? A) 24000 s (6 hrs, 40 min) B) 5400 s (1 hrs, 30 min) C) 8100 s (2 hrs, 15 min). D) 17100 s (4 hrs, 45 min). E) 13500 s (3 hrs, 45 min) 8. Consider our favorite 1.8 kg cube of side 1 m hanging on a string. As usual, I pluck the string with the cube hanging in air and hear a tone of 100 Hz. To commemorate my new home, I now put the cube in big vat of olive oil and pluck the string again. Now I hear a frequency of 50 Hz. What is the density of the oive oil? A) 1.15 times the density of water B) 1.80 times the density of water C) 1.60 times the density of water D) 1.50 times the density of water E) 1.35 times the density of water 9. The T-rex dinosaur in Robert Muldoon's side-view mirror, which is a convex mirror with a focal length of -50 cm, appears to be only 3 m tall. Muldoon knows the T-rex is right on their tail, about 2.5 m back from the mirror. How tall does he deduce the T-rex to actually be in this terrifying situation? A) 25 m. B) 6 m. C) 18 m D) 30 m E) 10 m. 10. A horizontal pipe will burst if its gauge pressure exceeds 10 atm. You have a feeder hose, open to the air, that shoots water into the pipe at 100 m/s. How much larger must the cross-sectional area of the pipe be than the area of the hose so that it doesn't burst? A) V3/2 times larger B) 3/y2 times larger C) 5/2 ies larger D) 2 times larger E) 5 times largerExplanation / Answer
7) density=2000kg/m³
Volume= 200*200*0.25=10000m³
Mass of asphalt=2000*10000=2*10^7 kg
Specific heat capacity=900J/kg/K
Increase in temperature=30
Power from sunlight= 1kW/m²*200*200m²=4*10^7 Watts
Total energy needed to increase the temperature by 30 degrees =(2*10^7)*900*30=5.4*10^11 Joules
Time needed by sunlight=(5.4*10^11)/(4*10^7)=13500 seconds=3.75 hrs=3 hrs 45 minutes
8)We know that the frequency of sound in string is proportinal to square root of tension in string
Initial tension in string=mass of block*g=1.8*9.8=17.64 N
Initial frequency=100Hz
Final frequency=50Hz
Final tension in string=17.64*50²/100²=4.41N
The reduction intension in string is because the olive oil exerts upwards buoyant force on the block which reduces the tension in string
Buoyant force experienced by block=17.64-4.41=13.23 N
Volume of block=0.1*0.1*0.1=0.001m³
Let density of olive oil be d
d*9.8*0.0001=13.23
d=1350kg/m³
Density of water =1000kg/m³
Therefore, density of olive oil=1.35 times density of water
9) image height=3m
Object distance=u=2.5m
Focal length=-50cm=-0.5m
Let image distance = v
1/v + 1/u=1/f
1/v +1/2.5=-1/0.5
v=-2.5/6 m
Magnification=v/u=1/6
Therefore,image size is 1/6 th times the object size
Therefore,object size=6*3=18m
10)let area of feeder be A1 and that of pipe be A2
Velocity of flow of water from feeder=100m/s
Velocity of water in pipe=100*(A1/A2)
Pressure at feeder=1 atm
gage pressure at feeder=0
Allowable Gage pressure at pipe = 10 atm=1000000N/m²|
Applying Bernoulli equation at pipe and feeder we get
0+(1/2)*1000*100² = 1000000+(1/2)*1000*(100*A1/A2)²
(A1/A2)²=0.8
A2/A1=sqrt(1.25)=sqrt(5/4)=sqrt(5)/2