Một đòn bẩy dài 1,5m. G là trọng tâm. Đầu A đặt vật 10kg, điểm tựa O cách A 50cm. Đòn bẩy hợp với mặt đất 1 góc 30°. Tìm lực tác dụng vào đầu B để đòn bẩy cân bằng trong các trường hợp sau : a, lực F có phương ngang
b, lực F thẳng đứng
c, lực F vuông góc với AB

Acoal-fired plant generates 600 mw of electric power. the plant uses 4.8 x 10^6 kg of coal each day, and the heat of combustion of coal is 3.3x 10^7 j/kg. the steam that drives the turbines is at a temperature of 300° c, and the exhaust water is at 37° c. (a) what is the overall efficiency of the plant for generating electric power? (b) how much thermal energy is exhausted each day? (c) what is the change in entropy of the universe for this heat engine? (d) using the same heat reservoirs, what is the maximum possible (carnot) efficiency for a heat engine?

The number of passengers who arrive at the platform of a subway station for the 10 am train is a random variable with a mean of 120 and a variance of 16. find the lower bound of the probability that there will be between 100 and 140 passengers (round off to second decimal place).

What happens to an isotope during radioactive decay?