The work done in displacing a load of mass m against the gravitation g through a height h is given by

w=mgh. Here the mass or load m= 10kg , g=9.81m/sec^2(assumed) and h = 4 metres.Threfore ,

w = (10g)(9.81m/s^2)(4m) =392.4 NM =392 joules

Therfore, the engine worked 500 joules, which resulted in a rsult of 392.4J

Therfore, the Effiency of the engine = (Resulted work/Actual work)*100

=(392.4/500)*100

=78.48%

w=mgh. Here the mass or load m= 10kg , g=9.81m/sec^2(assumed) and h = 4 metres.Threfore ,

w = (10g)(9.81m/s^2)(4m) =392.4 NM =392 joules

Therfore, the engine worked 500 joules, which resulted in a rsult of 392.4J

Therfore, the Effiency of the engine = (Resulted work/Actual work)*100

=(392.4/500)*100

=78.48%