(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Example 3.13 :

Example 3.1

2. Relevant equations

v=u+at

S=ut+1/2at^{2}

v^{2}-u^{2}=2aS

3. The attempt at a solution

I know the solution is in front of me, thats ok but I have a confusion regarding negative & positive signs. In both the examples something is moving vertically upwards & in both cases something is released below to the ground, then why in Example 3.13 initial velocity of the stone is taken as u = +12m/s whereas in Example 3.1 u = -2m/s ?

Also in Example 3.13, displacement = -65 m, why ?

Please clear these doubts of mine in as much detail as possible so that I know which sign to use in which case.

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# Homework Help: When to use negative sign ? [3 equations of motion]

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