A metal rod 50.000-cm long at 55.0 degree C is heated to 75.0 degree C. The leng
ID: 1475282 • Letter: A
Question
A metal rod 50.000-cm long at 55.0 degree C is heated to 75.0 degree C. The length of the rod is then measured to be 50.0264 cm. What is coefficient of linear expansion of the metal? A filament in alight dulb that dissipates heat at a rate of 100 W acts like a perfect blackbody (e = 1). What is the temperature of the hottest portion of the filament if it has a surface area of 6.3 Times 10^5 m^2? The Stefan-Bottzmann constant is 5.67 Times 10^8 W/(m^2 k^4). An engine is used to lift a 2500-kg truck to a height of 4.0 m at a constant speed. In the lifting process, the engine received 4.18 Times 10^5 J of heat from the fuel burned in its interior. How much work is done lifting the truck? What is the efficiency of the engine? A bell emits sound energy uniformly in all directions at a rate of 4.00 Times 10^-3 W. What is the intensity of the wave 100.0 m from the bell? The intensity of a spherical wave 2.5 m from the source is 120 W/m^2 What is the intensity at a point 9.0 m away from the source? A wave whose wavelength is 0.500 m is traveling down a 500-m long wire whose total mass is 25 kg and is under a tension of 2000 N. What is the speed of the wave on the wire? Find the frequency of this wave.Explanation / Answer
coefficient of linear expansion
alpha = (L2-L1)/(L1*dT)
alpha = ((50.0264-50)/(50*(75-55))
alpha = 2.64*10^-5 /oC
----------
from stefans law
P = sigma*e*A*T^4
100 = 5.67*10^-8*1*6.3*10^-5*T^4
T = 2300 K
t = T-273 = 2027 oC
------------------
3)
a)
W = m*g*h = 2500*9.8*4 = 98000 J
b)
efficiency = W/E = 98000/(4.18*10^5) = 23.4%
4)
intensity = power/area =P/4pir^2
I = (4*10^-3)/(4*pi*100^2)
I = 3.18*10^-8 W/m^2
B)
power of the source remains same
I2/I1 = (r1/r2)^2
I2/120 = (2.5/9)^2
I2 = 9.26 W/m^2
-----------
5)
v = sqrt(T/u)
u = linear density = m/L
v = sqrt(TL/m)
v = sqrt(2000*500/25)
v = 200 m/s
frequency f = v/lambda = 200/0.5 = 400 hz