Dear Albert, Thank you for your answers. Here are the next two: (1) See this equ

Question

Dear Albert, Thank you for your answers. Here are the next two: (1) See this equation: distance (d) = 1/2 (vi+ vf ) t. What the 1/2 represents? (2) When the gravity is noted as (- 9.81 m/sec2 ),I refer for the minus sign? Also related to this question let me know if I am right (seethe following): (a) Basically upward velocity is (+) ?                    downward  "        (- ) ? (b) Upward work by a force is (-)       Downward work by a force is(+) Please let me know about these question? Thank you for everything, Yours sincerely, Emeric Dear Albert, Thank you for your answers. Here are the next two: (1) See this equation: distance (d) = 1/2 (vi+ vf ) t. What the 1/2 represents? (2) When the gravity is noted as (- 9.81 m/sec2 ),I refer for the minus sign? Also related to this question let me know if I am right (seethe following): (a) Basically upward velocity is (+) ?                    downward  "        (- ) ? (b) Upward work by a force is (-)       Downward work by a force is(+) Please let me know about these question? Thank you for everything, Yours sincerely, Emeric

Explanation / Answer

I'm not Albert, but perhaps I can clarify some of these things. 1) The 1/2 is there in order to get the average of the twovelocities. Of course, this is only assuming a constantacceleration. 2) Upwards velocity will oftentimes be positive, while downwardvelocity will oftentimes be negative. However, that is not to saythat the opposite cannot be true. A good rule to remember is thatwhen you're dealing with vectors, signs don't matter much as longas you keep your system consistent. You can have a downwardvelocity as positive - just make sure that all downward velocitiesare positive and all upward velocities are negative. Same thing forforces.

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