During 3 hours one winter afternoon, when the outside temperature was 11°C, a house heated by electricity was kept at 20°C with the expenditure of 54 kwh (kilowatt·hours) of electric energy.

What was the average energy leakage in joules per second (watts) through the walls of the house to the environment (the outside air and ground)?

Explanation:

Since the temperature difference between inner and outside temperature remains constant , condition of steady state has been achieved . So heat produced is equal to heat leaked

heat leaked = heat produced

heat produced  = 54 kwh = 54 x 1000 x  60 x 60 J  

time taken  = 3 x 60 x 60 s

heat produced per second

= 54 x 1000 x  60 x 60 / 3 x 60 x 60

= 18000 J /s

heat leaked = 18000 J /s

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards