What part causes the disc brake caliper piston to retract when the brakes are released?

If anyone who can me with this hw? i would really appreciate it

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 photo above shows oil and vinegar in a pitcher. the top make a claim about about the density of the vinegar compared to the density of the oil summarize the evidence to support the claim and explain your reasoning