Projectile Motion


Projectile Motion


Projectile motion is one of the most interesting topics in JEE syllabus. This is the first topic which highlights how simple concepts (the equations of motion) can be combined to solve complicated problems (the analysis of projectile motion).


The most basic idea of a projectile motion is to realize that the motion consists of 2 simpler independent motions:

  1. Motion along X axis – this motion is a motion with a constant velocity. The gravity is acting vertically downwards and so, the component of velocity along x axis remains unchanged at all times
  2. Motion along Y axis – this motion is simply a motion under gravity with initial velocity equal to the component of velocity along the y axis.


Since these 2 motions are independent, the analysis becomes quite simple. All that is needed is the understanding of motion under gravity, which is nothing but a motion with constant acceleration. So, a good amount of practice will help you to solve the projectile motion problems with great ease.

Since projectile motion is fairly a simple concept, direct questions are not asked from this topic. Rather, questions asked generally involve a mix with some other concept such as work, power and energy or maybe even rotation. So, this chapter is essentially a “tool” to solve problems of other chapters and so, it becomes important to master projectile motion.

Projectile motion becomes tough when the problem involves a projectile motion along an inclined plane. However, for someone who has a good understanding of the basic projectile motion, projectile motion along an inclined plane is yet another instance of decomposition of a motion along 2 mutually perpendicular directions. The important point is to choose appropriate directions. The 2 directions that are generally chosen are:

  1. Motion parallel to the inclined surface of the inclined plane – a component of gravity acts along this direction. But since, the angle of inclination at all points is the same, this motion is simply a uniformly accelerated motion, similar to motion under gravity.
  2. Motion perpendicular to the inclined surface of the inclined plane – just like motion parallel to inclined plane, the motion perpendicular to the inclined plane is also a motion with a constant acceleration because the component of gravity perpendicular to the inclined surface of the inclined plane always remains unchanged.

This simple technique of decomposition always works like a charm. The difficult is usually in choosing the 2 independent direction. A rule of thumb – for projectile motion along the inclined plane, always choose the first direction to be parallel to the inclined plane and the second one to be perpendicular to the inclined plane.

Make sure to practice plenty of problems. Some times students are uncomfortable with angle calculations. It is important to spend time in calculating the angles correctly and then take appropriate sine and cosine components so as to avoid a silly mistake.

We hope this article helped you. Make sure to study Resnick Halliday Walker by Wiley publishers to gain a firm command over projectile motion.


About the Author

Aman Goel IIT B2 Aman Goel is B.Tech, computer science and engineering undergraduate student at Indian Institute of Technology, Bombay. Born in a business oriented family of Kanpur he secured an All India Rank 33 in JEE advanced 2013 and also scored 323/360 in JEE main 2013. He has also cleared Indian National Physics and Chemistry Olympiads, and KVPY. In his free time, he likes to write articles related to JEE preparation. He loves speedcubing (the art of speed solving a Rubik's cube) and also loves to play computer/mobile games.
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