Chứng tỏ rằng các trường véc tơ sau là trường thế và tính Z C
F · dR theo
đường cong trơn từng khúc nào đó nối A(10, −1), B(0, −1, 1).
a. F(x, y, z) = hsin z, −z sin yx cos z + cos yi
b. F(x, y, z) = h3x
2
y
2
z, 2x
3
yz, x3
y
2 − e
−z
i

Arefrigerator uses r-134a as the working fluid and operates on the ideal vapor-compression refrigeration cycle except for the compression process. the refrigerant enters the evaporator at 120 kpa with a quality of 34 percent and leaves the compressor at 70°c. if the compressor consumes 450 w of power, determine (a) the mass flow rate of the refrigerant, (b) the condenser pressure, and (c) the cop of the refrigerator. (0.00644 kg/s, 800 kpa, 2.03)