Who will tell me something about the physics problems in Grade Three?

Your answer is wrong: the rotating speed is 600r/min, and 1 min does work 300 times, so the working time cannot be calculated in 30 seconds (what does 30 seconds mean? Why not use 15 second? ), according to the 1960s, the result of correctly calculating power and efficiency should be half that of the standard answer.

The process is as follows:

(1) piston thrust F=pS=50N/cm? × 120cm？ =6× 10? n，

The piston reciprocates twice, does external work once and the crankshaft rotates twice.

Is the work done at a time W0=FL=3× 10? N×0.3m=900J，

The number of times the piston does work in 1 min is 600 times /2=300 times, and the work done in 1 min is W= 300×900J=270000J.

Diesel engine power p = w/t = 270000J/60s = 4500W = 4.5kW. ..

(2) If the diesel oil is 2Kg per hour, the diesel oil consumed per minute is m=2kg/60= 1/30kg.

Heat value of diesel oil: q diesel oil = 4.3×10.7j/kg.

The energy consumption of a diesel engine 1 min is Q=q, and the diesel engine m = 4.3×107j/kg×1/30kg =1.43×106j.

The efficiency of diesel engine η = w/q = 270,000J/1.43x106j =18.8%.