A Carnot cycle is to be designed to attain

efficiency of 0.75. It temperature of the

reservoir is 727°C, then low temperature

reservoir will have to be maintained at °C

reservoir is 727°C, then low temperature

Explanation:

Efficiency for any Heat engine = Work done by engine / Heat provided to the engine

Also, for a carnot engine derived formula for Carnot Engine

= 1 - T2/T1

Where, T2 = sink reservoir temperature

and T1 = source reservoir temperature

727° C = 1000 K

So, 0.75 = 1-T2 / 1000

So, T2 = 1000*0.25 = 250 K = - 23 Kelvin