Question

A reversible engine takes heat from a reservoir at ${527}^{o}C$ and gives out to the sink at ${127}^{o}C$ . The engine is required to perform useful mechanical work at the rate of 750W. How many calories per sec must the engine take from the reservoir ?

• A. 357.1 cal/sec
• B. 257.1 cal/sec
• C. 157.1 cal/sec
• D. 57.1 cal /sec

Answer 1

The correct option is A 357.1 cal/sec

Efficiency of the carnot engine$\left(\eta \right)=1-\frac{T_c}{T_h}$
$\eta =1-\frac{400}{800}=1-0.5=0.5$

also $\eta =\frac{W}{Q_h}$
$0.5=\frac{750}{Q_h}$
$Q_h=1500J/s=\frac{1500}{4.2}cal/s=357.14cal/s$
Option A.