When to Use Kg vs G in Physics Problems?

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In summary, the standard system of units includes the kilogram as the standard unit of mass. You can use either g or kg in a problem as long as your units are consistent. Acceleration and velocity can be positive or negative depending on the direction defined in the problem.
  • #1
pureouchies4717
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hi. i always thought that g was standard in all problems, until i started learning about tension and other forces, where kg is needed. can someone please clarify when i need kg and g? its for a test in an hour

also, when accel/velocity is pointing down, its negative right?
 
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  • #2
The standard system of units (called the SI units) actually includes the kilogram as the standard unit of mass. This standard unit system is often called the "meter-kilogram-second" or "mks" system.

You do not specifically need to use either g or kg in any specific problem; you just have to ensure that your units are consistent throughout the problem. If all of the quantities in a given problem are in kilograms, it's probably easier to use kilograms. If all the quantities in a given problem are in grams, it's probably easier to use grams. If some of the quantities in a given problem are in grams, and others in kilograms, you will need to ensure they are all in the same units (either g or kg, whichever you prefer), before continuing.

Acceleration and velocity are not universally defined in terms of "up" or "down." While it's conventional to use positive values for the "up" direction, and negative values for the "down" direction, problems can be worded in the opposite sense. A well-written problem should include information about which direction is represented with which sign, like the following:

a rocket launched upwards with an acceleration of +5 m/s2...

- Warren
 
  • #3
thank you

so, when velocity and acceleration are in oppposite directions, that it is the only time that they need to be separate signs, right?
 

1. How do kilograms and grams differ?

Kilograms (kg) and grams (g) are both units of measurement for mass. Kilograms are larger and typically used for larger objects, while grams are smaller and typically used for smaller objects.

2. When should I use kilograms?

Kilograms should be used when measuring the weight of larger objects, such as people, animals, or heavy items like furniture. It is also the standard unit of measurement for mass in scientific experiments and calculations.

3. When should I use grams?

Grams should be used when measuring the weight of smaller objects, such as food items, jewelry, or medication. It is also commonly used in cooking and baking recipes.

4. Can I convert between kilograms and grams?

Yes, you can convert between kilograms and grams by using the conversion factor of 1 kg = 1000 g. To convert from kg to g, multiply the number of kilograms by 1000. To convert from g to kg, divide the number of grams by 1000.

5. Why do we have both kilograms and grams as units of mass?

Kilograms and grams are both used as units of mass because they provide a range of measurement options for different types of objects. Kilograms are more practical for larger objects, while grams are more practical for smaller objects.

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