Suppose I have a projectile and launch it with an oblique velocity, meaning it has both horizontal and vertical components of velocity.
Neglecting air resistance and the like, it’s trajectory should look like what I drew-
Here the red arrow is the downward constant acceleration, the green arrow is the net velocity (vector sum of its components) and the angle between the acceleration and velocity I have marked in yellow.
I have filled in the angle in the regions where I think the angle between the velocity and the acceleration would be acute, which I think is the entirety of the projectile motion after it crosses its maximum height till it reaches the ground again.
However, on searching the net and also from a question paper I saw, it states the the angle between velocity and acceleration is minimum and acute at only one point.
Why is it only one point? Does the ‘minimum’ word have anything to do with it? I thought the angle would be acute over a number of points in the second half of the projectile’s motion.
Best Answer
The angle will be acute for whole second half of the projectile motion but will be minimum and acute ( both same time) at the point where ball just strikes the ground.
It will be maximum and obtuse just as you launch the ball.
Note that angles which are minimum and obtuse and maximum and acute does not exist.