We are discussing relative speed concept where the platform is moving as well.
In this case, if the object on the platform moves in the same direction as the platform, the speeds are added up, while moving in the opposite dorection of the platform, speeds are subtracted (Imagine rowing a boat agains the water current and along with water currents, while going against, it is tougher to row as the forces are opposing, while going along, it's easier as the current helps rowing).
Coming to question:
We use distance = speed * time,
Carla: Total distance covered = 200 meters = 1.5*40 + x*0.5 + 2*5, (where the first term represents the distance covered when Carla was running 1m/s + 0.5m/s(speed of platform) for 40 seconds, the second term is where she is still so total speed is just speed of platform which is 0.5m/s for x seconds, next third term is where she is running at 1.5 m/s + 0.5m/s for 5 seconds), gives us x as 260 seconds
Daniel: Total distance covered = 200 meters = 1*y, (Daniel walks at 0.5 m/s + 0.5 m/s(speed of the platform), for y seconds to cover a total distance of 200 meters), gives us y as 200 seconds
So, 260 and 200.
Bunuel
In a certain mega-shopping mall, Carla and Daniel start from the beginning of a 200-meter-long moving walkway and move in the same direction as the walkway, which travels at a constant speed of 0.5 meters per second.
- Carla starts running at a constant rate of 1 meter per second relative to the walkway, continues running for exactly 40 seconds, and then stops running for x seconds. While not running, Carla stands still and is carried only by the walkway.
- Afterward, she resumes running at 1.5 meters per second relative to the walkway for exactly 5 seconds, at which point she reaches the end of the walkway.
- Daniel walks at a constant rate of 0.5 meter per second relative to the walkway, from start to finish without stopping, and reaches the end in y seconds.
Select for
x and
y the value of of x and y, that are consistent with the information provided. Make only two selections, one in each column.