An iron block of mass m = 500 g is dropped from a height h = 20 meters above ano

Question

An iron block of mass m = 500 g is dropped from a height h = 20 meters above another iron block of mass M = 1 kg. The bottom block sits on the floor, but it is thermally isolated from the floor. Iron (Fe) has an atomic weight of 56 g/mole. (You can find all atomic weights in the Periodic Table ) Initially, the two blocks have a temperature Ti = 27o C.
Use g = 9.81 m/sec2 and 0o C = 273 K

2)
Is the process described above reversible?

a.Yes b.No c.Sometimes


3)In the Lecture examples illustrating the equipartition of energy, we saw how much thermal energy there is in a gas or a solid with N atoms at temperature T. What is the total initial thermal energy, U, of the smaller block of mass m =500 g, at the initial temperature Ti = 27o C ?
U=


4)
Take the volume V of the block of iron of mass m = 500g, but filled with nitrogen, N2, at pressure p = 1 atm = 1.01 105 Pa, and temperature T = 27o C. The density of iron is 7.9 g/cm3. Nitrogen is a diatomic gas with molecular weight = 28g/mole. How many iron atoms NFe are there in the 500 g block compared with the number of nitrogen molecules NN2 in the same volume V ?

The ratio of the number of iron atoms to the number of nitrogen molecules, NFe/ NN2 is closest to



5)
How does the thermal energy of the 500 g iron block compare with the thermal energy = total kinetic energy, KE, of the same volume of nitrogen ? Let pressure p = 1.01 105 Pa, temperature T = 27o C.


Thermal energy of the iron is

a.much larger than KE of the same volume of nitrogen
b.about the same (within a factor of 2) as the KE of the same volume of nitrogen
c.much smaller than KE of the same volume of nitrogen

An iron block of mass m = 500 g is dropped from a height h = 20 meters above another iron block of mass M = 1 kg. The bottom block sits on the floor, but it is thermally isolated from the floor. Iron (Fe) has an atomic weight of 56 g/mole. (You can find all atomic weights in the Periodic Table ) Initially, the two blocks have a temperature Ti = 27o C. Use g = 9.81 m/sec2 and 0o C = 273 K 1)Assume that the kinetic energy of the falling block is transformed entirely into internal thermal energy when the falling block stops. What is the change in the internal energy, ?U, of the system? ?U = 2) Is the process described above reversible? a.Yes b.No c.Sometimes 3)In the Lecture examples illustrating the equipartition of energy, we saw how much thermal energy there is in a gas or a solid with N atoms at temperature T. What is the total initial thermal energy, U, of the smaller block of mass m =500 g, at the initial temperature Ti = 27o C ? U= 4) Take the volume V of the block of iron of mass m = 500g, but filled with nitrogen, N2, at pressure p = 1 atm = 1.01 105 Pa, and temperature T = 27o C. The density of iron is 7.9 g/cm3. Nitrogen is a diatomic gas with molecular weight = 28g/mole. How many iron atoms NFe are there in the 500 g block compared with the number of nitrogen molecules NN2 in the same volume V ? The ratio of the number of iron atoms to the number of nitrogen molecules, NFe/ NN2 is closest to 5) How does the thermal energy of the 500 g iron block compare with the thermal energy = total kinetic energy, KE, of the same volume of nitrogen ? Let pressure p = 1.01 105 Pa, temperature T = 27o C. Thermal energy of the iron is a.much larger than KE of the same volume of nitrogen b.about the same (within a factor of 2) as the KE of the same volume of nitrogen c.much smaller than KE of the same volume of nitrogen

Explanation / Answer

m = 500 g = 500 * 10^-3 kg
h = 20 meters
M = 1 kg
the potential energy of the falling block is
U = mgh --------(1)
where g = 9.8 m/s^2
we know from the relation
U = m * s * delta(t) --------(2)
where s is specific heat of iron and delta(t) = t_f - t_i
t_i = 27 oC = 27 + 273 K = 300 K
from (1) and (2)
mgh = m * s * delta(t)
or gh = s * delta(t)
solving above for t_f we get the final temperature

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