Which of the following is not true about energy conversion devices?

a. total energy input = useful energy output
b. total energy input = total energy output
c. total energy input = useful energy output + energy dissipated to the surroundings
d. total energy input = total energy output / efficiency

In what direction does an applied force move an object

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).

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.