a) The acceleration is in 90degree angle to the motion
b) The object is stationary, but accelerating
c) The resultant force is 0, but the object is moving作者: abc666 時間: 18/6/2007 09:17 AM b)設一物件向前行的速度是正,該物件一開始向後移動,然後向前加速,速度由負數到正數中經過速度是0的一瞬間,該物件是不動的,但在加速中 Let the speed of he object when moving backward be negative. At the begining, the object is moving backward. then it accelerate forward.when the speed of the object changes from negative to positive, it pass through a point that the speed is 0. At that time, the object is stationary, but accelerating.作者: sapphire 時間: 18/6/2007 10:09 AM 比起HKALE實在是不夠看orz
a) Consider an object moving in a circular path. Its acceleration is always towards the centre of the path, and its direction of motion is tangential to the circular path. So its acceleration is always perpendicular to its direction of motion.
c) Consider a rod resting on a table. Then two forces, equal in magnitude but opposite in direction, are acted on the two ends of the rod, in the direction perpendicular to it. The resultant force acting on the rod is zero, but there is a torque causing the rod to have a turning motion.
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