An object with mass 0.05 kg is falling downwards under the influence of g.Find the force acting on it? .take g 10m/s2 Now answer me why should we take g 10 not -10

1 Answer
Steve J.
Aug 18, 2017

It is a matter of how the reference system is defined.

Explanation:

Since the problem gives you #g = 10m/s^2#, the problem is defining the reference system with the positive direction being down. With that definition, the value of the acceleration due to gravity is positive.

And when you use Newton's 2nd Law (F=ma) to calculate the force, you must give the result as positive because the force also points down.

The assignment of polarity of directions in a reference system is optional. When a problem allow you to choose, the direction that you choose to consider the positive direction of the reference system will not change the conclusion.

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