Two aircraft are flying directly away from each other with equal speed. Each
aircraft emits a sound pulse which is
picked up by the other aircraft. What
speed (km/hr) must each aircraft have in
order that the arriving pulse has a frequency one fifth the emitted frequency?
[ ? ] km/hr
Hint: The speed of sound is 343 m/s.

Idon’t quite understand this problem

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).

The junction rule describes the conservation of which quantity? note that this rule applies only to circuits that are in a steady state.