Let's explore the differences between the choices:
A kilogram is a unit of mass, not weight. Mass is a measure of the amount of matter in an object and remains constant regardless of the object's location in the universe. The SI unit for mass is the kilogram (kg). So, one kilogram represents a certain amount of mass, not weight.
A kilojoule is a unit of energy, not weight or mass. It is commonly used to measure energy content in food and the energy released in various chemical reactions. The joule (J) is the SI unit of energy, and a kilojoule (kJ) is equal to 1000 joules.
A kilometer is a unit of distance or length, not weight or mass. It is equal to 1000 meters. Kilometers are commonly used to measure distances on roads, tracks, or geographical features. The kilometer (km) is a unit of the metric system for measuring lengths and distances.
A kilonewton is a unit of force, specifically, it is a measure of weight in the context of force due to gravity. One kilonewton is equal to 1000 newtons. Weight is the force exerted by gravity on an object, and it varies depending on the gravitational field strength. The kilonewton (kN) is often used in engineering, particularly in structural and mechanical contexts where forces need to be measured or applied.
To sum it up:
- A kilogram is a unit of mass.
- A kilojoule is a unit of energy.
- A kilometer is a unit of distance.
- A kilonewton is a unit of force or weight.
The correct answer to the question "Which unit is a unit of weight?" is option D kilonewton.