1. A 1.5 kg block is connected to a horizontal spring whose constant is 2.5 N/m.
ID: 1288456 • Letter: 1
Question
1. A 1.5 kg block is connected to a horizontal spring whose constant is 2.5 N/m. The block is pulled to the right a distance of 4 cm and then released. a) What is the amplitude of oscillation? b) What is the period for one oscillation? c) What is the equation describing its motion? (hint- use initial conditions) 2. A crying child produces a sound level of 90 db at a distance of 1.2m. What is the intensity in dB at a distance of 800 m? 3. Suppose the temperature of a liquid is 350 Kelvins. What is this in Fahrenheit? 4. 70L of oxygen at 20 C has a pressure of 2.5 atmospheres. a) How many molecules of oxygen are there? b) What is the mass of oxygen present in grams? 5. Suppose a freezer has a coefficient of performance of 4.0 and uses 200 watts. If a tray of water is placed inside and the temperature of the water is 0 C, how much water in grams can be frozen in 2 minutes? (latent heat of fusion = 80 cal/g)Explanation / Answer
1)
a) A = 4 cm
b) w = sqrt(k/m)
T = 2*pi/w
= 2*pi*sqrt(m/k)
= 2*pi*sqrt(1.5/2.5)
= 4.86 s
c)
x = A*cos(w*t)
= 4*cos(4.86*t)
2)
beta1 = 10*log(I1/Io)
90 db = 10db*ln(I1/10^-12)
9 = log(I1/10^-12)
I1 = 10^(9-12)
= 10^-3 W/m^2
we know,
I2/I1 = (r1/r2)^2
I2 = I1*(r1/r2)^2
= 10^-3*(1.2/800)^2
= 2.25*10^-9 w/m^2
beta2 = 10*log(I2/Io)
= 10db*log(2.25*10^-6/10^-12)
= 63.5 dB <<<<<<<---------Answer
3)
we know,
Tc = Tk - 273
= 350 - 273
= 77 degrees centigrade
now use the relation,
Tc = (5/9)*(Tf-32)
Tf = (9/5)*Tc + 32
= (9/5)*77 + 32
= 170.6 faurenheight degrees
so, 350 k = 170.6 faurenheit degrees
4) n = P*V/(R*T)
= 2.5*1.013*10^5/(8.314*(273+20))
= 104 moles
a) N = n*Na
= 104*6.023*10^23
= 6.234*10^25
b) m = n*M
= 104*32
= 3328 grams
= 3.328 kg
5) Q = 2*60*200/4 = 6000 J
Q = m*Lf
==> m = Q/Lf
= 6000/(80*4.18)
= 17.9 grams
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