Thermodynamics ...

In above shown figure of refrigeration system. Which of the following statement explains why work is an input into this system?

In a thermodynamic processes during each cycle , a heat engine absorbs 400 J of heat from a higher- temperature source and release 300 J of heat to the low-temperature sink. Calculate the efficiency of heat engine?

A heat engine takes in heat at 750 degrees Celsius and expels heat at 250 degrees Celsius. What is this engine's theoretically ideal (Carnot) efficiency?

Find out the efficiency of the heat engine if it produces $$100 J$$ of heat, does $$30 J$$ of work, and emits $$70 J$$ into a cold reservoir.

A heat engine produces 100 J of heat, does 30 J of work, and emits 70 J into a cold reservoir. What is the efficiency of the heat engine? 

The idealized P-V diagram above shows a complete cycle through compression and expansion of a gas. The questions below relate to the processes within the cycle.
Which letter shows work done?

During a cyclic thermodynamic process, a gas absorbs 45 J of heat.
Which table correctly describes the change in internal energy in the gas and work done by the gas during this cycle?

The thermal capacity of $$10$$gm of the substance is $$8$$ calories. Then its specific heat is.

For a particular heat engine, 3,000 J of energy goes in at 700 K and 2000 J comes out at 200 K. The rest of the energy is used work.
What is the actual efficiency of this engine?

A liquid is being converted into vapours at its boiling point the specific heat of the liquid at this temperature will be.