The picture shows the cable car seen in Xiaohong's trip. Xiaohong wants to estimate the mechanical efficiency of the cable car. She found the beginning and end of the cable car from the map.

(1) Mountain gravity: g1= m1g =15× 60kg×10n/kg = 9000n;

Downhill gravity: G2 = M2g = 8× 60kg×10n/kg = 4800n;

Lifting height of cable car h=840m-230m=6 10m,

Then the cable car has done useful work: w useful = (g1-G2) h = (9000 n-4800 n) × 610m = 2.562×106j,

Answer: The useful work done by the cable car is 2.562× 106J. j .

(2) According to the problem, the actual power of the motor is: p real =ηP quantity =45000W×60%=27000W, t=7min=420s,

Then the total work actually done by the motor: WTotal = PRERTT = 27000W× 420s =1.134×107j,

Answer: The total work actually done by the motor is1.134×107 J.

(3) The mechanical efficiency of the cable car is: η=W total useful w×100% = 2.562×106j134×100% ≈ 22.6%,

A: The mechanical efficiency of the cable car is 22.6%.