(URCA 2015) - Question Medium of Physics

In an experiment conducted in the Physics Laboratory, a group of students found that a wooden block floated in water with half of its volume submerged. Next, the same block was placed in oil where they found that it floated with $$\frac{1}{4}$$ of its volume emerged. From this information, we can affirm that the specific mass of the oil is:

The city of Salvador, famous for its hills and elevators, is a perfect example to demonstrate the force of traction. The Lacerda Elevator, one of the main postcards of the city, transports thousands of people daily between the Upper Town and the Lower Town. Suppose one day, a group of 15 people with an average mass of 70kg decide to use the elevator at the same time. Considering the elevator's mass as 500kg and the acceleration due to gravity equal to 10 m/s², what would be the traction force on the elevator cable when it is at rest or moving at a constant speed?

A motor operates according to the Carnot cycle between two thermal sources. The hot source is at a temperature of 500 K and the cold source at 300 K. Determine the efficiency of the motor, knowing that the efficiency of the Carnot cycle is calculated by the expression 1 - (Tcold/Thot), where Tcold and Thot are the temperatures of the cold and hot sources, respectively. Discuss briefly the importance of the maximum efficiency of the Carnot cycle in practical applications of thermal engines.

Your image O' and five observers: 1, 2, 3, 4, 5. Which alternative presents only the observers who see the object reflected in the mirror?