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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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 yeungwk91 版主 發短消息 加為好友 當前離線 2# 大 中 小 發表於 2016-2-20 02:56 PM (第 606 天) 只看該作者 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 UID182785 帖子3731 精華0 積分549 閱讀權限100 在線時間4722 小時 註冊時間2010-10-8 最後登錄2017-10-17  查看詳細資料 TOP

## 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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