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[Phy] some concept questions

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some concept questions

1. vector question
if R is vector , then R=Rx+Ry
if R is scalar, then R^2= Rx ^2 + Ry ^2

however, when I need to find the magnitude of force, why use R^2= Rx ^2 + Ry ^2? ( as I think force is a vector)

if the queston ask me to find the final velocity of an object, should I use  R=Rx+Ry or R^2= Rx ^2 + Ry ^2?

2.Does the airplane flying on sky have normal reaction force?

3. in circular motion, is tangential acceleration equals to  instantaneous velocity of an object?
   

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2) You may call it normal reaction in DSE or Upthrust

3) tangential acceleration is responsible for accelerating / decelerating.
    = rate of change of speed.

1) force is a vector definitely.
the magnitude of force is a scalar.

The Q asks for final velocity => it means the magnitude of velocity

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回覆 2# yeungwk91 的帖子

but as far as i know, normal reaction exist when an object is on a surface
but when airplane is flying and it dont touch the surface,  why it has normal reaction?

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回覆 3# lightthefuture 的帖子

It is about fluid mechanics

The force should be called Upthrust.
It is acting on the plane by the air surrounding.

Just for DSE, u mark it as normal reaction ( that's fine)

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