Define the term ‘projectile motion’. Show that the path of any projectile
launched at an angle to the horizontal is a parabola. A football is thrown in a
parabolic path. Is there any point at which the acceleration is perpendicular to
the velocity? If yes, where
Answers
Answer:
It is a classical question of parabolic motion and i recall my NCERT lessons during my 11th standard.
When a ball is kicked, the ball is provided motion which is at a certain angle to the horizontal plane. Assuming that there is no air drag considered into the picture, if we break the motion into horizontal and vertical components, there is no horizontal acceleration since no force acts in that direction. Whereas, there is a vertical acceleration (downward) in the form of gravity.
As the ball ascends, it faces a deceleration due to gravity until its upward vertical motion stops momentarily and then it starts to descend with gravity favoring the downward motion.
Without going into equations of motion, it can be easily visualised that the ball reaches its highest vertical point where the vertical motion stops momentarily.
Now, the only acceleration is due to gravity and it acts vertically downwards (@90deg to horizontal).
The horizontal component of velocity remains constant at all times since there is no horizontal acceleration to change it as discussed above. This is always perpendicular to the acceleration due to gravity.
The vertical component of velocity is the only one which is parallel to the acceleration due to gravity and as soon as it becomes zero, the only component which remains is horizontal.
This phenomenon occurs when the football reaches max height.
Thus, at max height, velocity is perpendicular to the acceleration (due to gravity) when the ball is kicked from a horizontal surface at some angle to the horizontal.
Explanation: