kinematics!!!!!!!!!!! HELP

[lisafaustina]

hi so i'm doing these constant acceleration questions and when you get a question like throwing a ball up in the air, it seems like sometimes you have to put in a= -9.8m/s^2 and sometimes its a=9.8m/s^2 . i thought when youre dropping something from up in the air you dont put a negative sign in front of the acceleration...but some questions contradict my theory :S
can somebody please clarify when you should put acceleration as negative? ive got a sac tomorrow HELP

[Whatlol]

Well it depends how you look at it, when the ball is going upwards, its acceleration will be -9.8m/s^2 because its velocity is decreasing, however on the way down it will be gaining velocity.

[98.40_for_sure]

Doesn't matter if it's positive or negative... as long as you use it consistently throughout the entire question, you should get the same answer?

[lisafaustina]

Well it depends how you look at it, when the ball is going upwards, its acceleration will be -9.8m/s^2 because its velocity is decreasing, however on the way down it will be gaining velocity.

so on the way up its negative, and on the way down its positive?
if its the same question

[Whatlol]

Well it depends how you look at it, when the ball is going upwards, its acceleration will be -9.8m/s^2 because its velocity is decreasing, however on the way down it will be gaining velocity.

so on the way up its negative, and on the way down its positive?
if its the same question

Hmm it kind of depends on the question and also what you treat the final and positive velocities as... but i dont do specialist so i wont say anymore (=

[jasoN-]

If it's slowing down, it indicates a negative acceleration (sign of acc = -(sign of vel) [ie. opposite])
Speeding up indicates a positive acceleration (sign of acc = sign of vel)
So if a ball is being thrown up, its velocity is decreasing (slowing down), hence acceleration is negative

[TrueTears]

hi so i'm doing these constant acceleration questions and when you get a question like throwing a ball up in the air, it seems like sometimes you have to put in a= -9.8m/s^2 and sometimes its a=9.8m/s^2 . i thought when youre dropping something from up in the air you dont put a negative sign in front of the acceleration...but some questions contradict my theory :S
can somebody please clarify when you should put acceleration as negative? ive got a sac tomorrow HELP

The sign can be either, it all depends how you define your directions.

Say if you let up be positive and down be negative, then since acceleration is pointing down, it would be negative.

If you let up be negative and down be positive, then acceleration is positive.

You must follow what you defined throughout the whole question.

[fady_22]

Well it depends how you look at it, when the ball is going upwards, its acceleration will be -9.8m/s^2 because its velocity is decreasing, however on the way down it will be gaining velocity.

so on the way up its negative, and on the way down its positive?
if its the same question

This is wrong. The direction of the acceleration here remains constant, but depending on what you define as positive (usually up or down), it can be positive or negative.