How much time is needed to produce 720 joules of work if 90 watts of power is used

8 seconds

Explanation:

power (P) is defined as the rate at which work is done.

power is measured in Watts (W) , when the work done is measured in Joules (J) and time in seconds

by the definition of power,

Answer : The correct option is, (b) 91 %

Solution :

Efficiency of the heat engine : The ratio of work done by the system to the amount of heat transferred to the system at the higher temperature.

Formula used :

where,

= efficiency of heat engine

= work done

= cold temperature = 160 K

= hot temperature = 1800 K

= input heat

Now put all the given values in the above formula, we get the efficiency of the heat engine.

Therefore, the efficiency of the heat engine is, 91 %.