Question
solve 40 please
A mass of 5 kg undergoes a process during which there is heat transfer from the mass at a rate of 10 kJ per kg, an elevation decrease of 75 m, and an increase in velocity from 10 m/s to 20 m/s. The specific internal energy decreases by 10 kJ/kg and the acceleration of gravity is constant at 9.8 m/s^2. Determine the work for the process in kJ. As shown in Fig. P2.40. 5 kg of steam contained within a piston-cylinder assembly undergoes an expansion from state 1, where the specific internal energy is u_1 = 2, 709.9 kJ/kg, to state 2, where u_2 = 2, 659.6 kJ/kg. During the process, there is heat transfer to the steam with a magnitude of 80 kJ. Also, a paddle wheel transfers energy to the steam by work in the amount of 18.5 kJ. There is no significant change in the kinetic or potential energy of the steam. Determine the energy transfer by work from the steam to the piston during the process in kJ.
Explanation / Answer
given Q = 80 kJ ,
m = 5 kg ,
u1 = 2709.9 k J
u2 = 2659.6 kJ
Wpaddle wheel = 18.5 kJ
using equation
Wpiston = Q - m ( u2 - u1 ) - Wpaddle wheel
= { 80 - 5 X ( 2659.6 - 2709.9 ) - ( - 18.5 ) } in K J
= { 80 - 5 X ( 2659.6 - 2709.9 ) - ( - 18.5 ) } X 103
= { 80 + 251.5 + 18.5 } X 103
= 350 X 103 J
or
Wpiston = 350 kJ
