Which of the following is a unit of distance? Kelvin, kilogram, second, meter.
Distance is a physical quantity. And the result of a measurement of a physical quantity is a value and an associated unit. The question is asking us which of these four units is an appropriate unit to use when reporting a measurement of distance. So let’s look at these four units.
The first unit is kelvin. Kelvin is not a unit of distance, it is a unit of temperature. If we don’t recall this off hand, we may recall other times when we use the unit kelvin in the context of temperature. For example, room temperature is typically taken to be about 298 to 300 kelvin. Since we are reporting a temperature with units of kelvin, we know that kelvin is a unit of temperature.
Kilograms are also not a unit of distance; they are a unit of mass. This unit is common on many household scales. Another common unit on household scales, especially for those used in food preparation, is the gram, which is one one thousandth of a kilogram. We may also recall the scientific fact that one liter of water has a mass of one kilogram, which tells us immediately that the kilogram is a unit of mass.
What about our third choice, the second? The second is also not a unit of distance. The second is a unit of time. We may recall, for example, that a stopwatch, which measures time, counts in seconds. By process of elimination, this leaves us with the meter as a unit for distance. And indeed, a common tool for measuring distance is the meter stick, which is so named because it has a length of one meter.