Thermodynamics : 1. An ideal gas in a horizontal piston is initially at 300K and

Question

Thermodynamics :

1. An ideal gas in a horizontal piston is initially at 300K and 20 atm. The gas undergoes a process whereby the gas is initially at 300 K and 25 atm. How much work is done in Joules.

2. You have been asked to testify as an expert witness in a court case. It seems that as a practical joke, two kids were dropping gravel from a window 125 ft (approximately 10 stories) above street level at people passing by. A lady claims to have had her arm broken by a piece of gravel. You have been asked to testify as an expert witness.

a) Determine the velocity of the piece of gravel upon impact in miles per hour and the force of the impact in Newtons. Assume that her arm was 4ft from the ground and that the grael weighed 150 grams

b) From this information, would you testify to her claim being true or faulse? It takes approximately 50,000 N to break a human bone.

Explanation / Answer

1.
you must give the number of moles of gas.
I am assuming its n

W= n*R*T ln(Vf/Vi)

Since,
T is constant.
PiVi = PfVf
20*Vi = 25*Vf
Vf/Vi = 0.8

putting this value in above equation:
W= n*8.314*300* ln(0.8)
   = -556.6 n joule

2.a)
1 ft = 0.3048 m
height through which ball travells = (125-4) = 121 ft = 121 *0.3048 = 36.9 m
Vf ^2 =vi^2 + 2*g*h
      = 0^2 + 2*9.8*36.9
Vf = 26.9 m/s
    = 26.9*3600/1000 km/hr
    =96.8 km/hr
    =96.8*0.621371 miles/hr
    = 60.15 miles/hr

F= m*g
=(0.15 kg)*(9.8 m/s^2)
= 14.7 N

b)
since force calculated baove is less: It will not break her bone

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