標題: [Phy] some concept questions [打印本頁] 作者: lightthefuture 時間: 2016-2-20 02:25 PM 標題: 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? 作者: yeungwk91 時間: 2016-2-20 02:56 PM
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 作者: lightthefuture 時間: 2016-2-21 12:07 AM 標題: 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? 作者: yeungwk91 時間: 2016-2-21 12:18 AM 標題: 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)