Why is the efficiency of a machine never 100%

Two football players with mass 75kg and 100kg run directly toward each other with speeds of 6 m/s and 8 m/s respectively, If they grab each other as they collide, the combined speed of the two players just after the collision would be:

A combined circuit has two resistors in series (27.5 ohms and 33.0 ohms) and another in parallel (22.0 ohms). If the power source is 9.0 volts, what will the current be? A. 0.062 amps B. 16 amps C. 0.56 amps D. 0.32 amps E. 39 amps

American football is played on a 100 yd100 yd long field, excluding the end zones. What is the length? L of the field in meters? Assume that 1 m equals 3.281 ft. 3.281 ft.

Exhaust outlets are often located in the area under a boat's swim platform. this area should be strictly off limits. what is the danger if a swimmer enters this area?

Quais são os agentes propulsores utilizados para gerar energia elétrica nas termoelétricas e nas hidrelétricas?

Show that the Newton has the units of mass times acceleration.

Light travels at 150000000km from the sun to earth in 8 minutes. What speed is this in Km/s

Electricity problem (coulomb's law)

An observer (O) spots a plane (P) taking off from a local airport and flying at a 29° angle horizontal to her line of sight and located directly above a tower (T). The observer also notices a bird (B) circling directly above her.

In order for convection to occur, you must have