Question
1. MULTIPLE CHOICE QUESTION Why must we use the constant motion equation for horizontal motion?Check all that apply. Acceleration due to gravity only affects vertical motion and not the horizontal motion of the projectile The projectile does not accelerate in the horizontal direction. As long as air resistance is negligible.
Answer
4.3
(204 Votes)
Rupert
Master · Tutor for 5 years
Answer
A, B
Explanation
The key to answering this question lies in understanding the fundamentals of two-dimensional motion, especially as pertaining to the motion of projectiles. In projectile motion, the motion along the vertical and horizontal axes is decoupled. This is largely an effect of the fact that, assuming there is no air resistance, the only force that is acting on the projectile whilst in flight is due to gravity which acts vertically downwards. Therefore, vertical motion is subject to gravity—seen as an acceleration, and takes the form of upward initial motion followed by downwards motion after the peak height is reached. In contrast to this, horizontal motion is constant—there is neither a horizontal force nor hence acceleration. The speed in the horizontal direction remains constant throughout the flight. The absence of a horizontal acceleration is critical in realizing why we use the "constant motion" equation for horizontal motion.When taken together, these parallel motions (constant horizontal speed because there's no acceleration, accelerated vertical motion due to gravity that changes from upward to downward over time) give the classic, parabolic traces we associate with projectiles.