vertical accelerations

[AntonFreeman]

My question regards to TBR physics review part 1 question 65 for translational motion passages. If ball A is moving same direction as the gravity, and ball B is moving in opposite direction of gravity, shouldn they have different vertical accelerations? I understand that their magnitude of acceleration will be same but they have different signs. The book explains that they should have same vertical accelerations even though they state that one is speeding up and one is slowing down. Thanks in advance.

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[Halfling]

My question regards to TBR physics review part 1 question 65 for translational motion passages. If ball A is moving same direction as the gravity, and ball B is moving in opposite direction of gravity, shouldn they have different vertical accelerations? I understand that their magnitude of acceleration will be same but they have different signs. The book explains that they should have same vertical accelerations even though they state that one is speeding up and one is slowing down. Thanks in advance.

Hey...

You are confusing Vertical acceleration with Vertical Velocity.

The vertical acceleration is due to the Force (in this case, the force due to gravity which will act downwards in both cases).

So, For the ball going in the direction of gravity:
The vertical acceleration is g
The vertical velocity is v

For the ball going in the opposite direction of gravity:
The vertical acceleration is g
The vertical velocity is -v (notice different sign here)

*** Acceleration is due to the Force (F=ma)

Hope that helps

 

[BerkReviewTeach]

Well explained Halfling!

This is a really common mistake and one that seems to be exploitable by MCAT test writers.

If you think about it this way, it might help. When you throw a ball up, it will gradually slow down, stop for an instantaenous moment, and then come back down. So it goes from being the ball going up (Ball B) to the ball going down (Ball A). The direction of gravity never changed during the process, so it must be the same for the entire pathway. Does this perspective help at all?

 

[AntonFreeman]

yea it makes sense. thanks for your explanations guys.

 

[WhiteWashed]

yea it makes sense. thanks for your explanations guys.

verticle accel is always 9.8 no matter if its going up down or sideways. ...unless its on a ramp and unless there is a normal force...