Answer to Question #264010 in Mechanical Engineering for Neilmar

Question

Assume 2 kg of hydrogen (Item B 28) are initially at 40 atm, 100 K. (a) If the hydrogen changes pressure to 1 atm without a change of temperature, find the changes of enthalpy and entropy. (b) If the hydrogen changes temperature to 35 K with no change of entropy, find the change of pressure and enthalpy.

Answer 1

a-

Velocity of the ball at maximum height is zero, v=0

$v ^2 −u ^2 =2aH$

$0−(49) ^2 =2×(−9.8)×H$

H=122.5 m   

b-

v=u+at

0=49−9.8t

t=5s

Total time taken by ball to return to the surface, T=2t=10 s