Class 11 · Chapter 6
Centre of Mass & Collisions
Overview, notes, short notes, formula sheet, daily practice problems, previous year questions, and videos for this chapter — all in one place.
Centre of Mass & Collisions JEE Notes
Fully worked, JEE-style problems on variable mass systems, oblique collisions, and momentum conservation — the multi-step setups JEE Main and JEE Advanced actually test, going a level beyond the regular DPP.
A rocket with initial mass 1200 kg is launched vertically upward from rest. It burns fuel at a constant rate of 10 kg/s and ejects it downward at 2500 m/s relative to the rocket. Find the rocket's velocity 60 s after launch. (g = 10 m/s²)
Two identical balls undergo an oblique elastic collision; one ball is initially at rest. After the collision, the ball that was originally moving travels at 30° from its original direction. At what angle does the previously-stationary ball move?
A uniform chain of linear mass density 0.5 kg/m is held vertically with its lower end just touching the ground, then released. Find the normal reaction force from the ground on the pile of fallen chain when it has fallen through a height of 2 m and its falling end has speed 4 m/s. (g = 10 m/s²)
A bomb at rest explodes into two fragments of mass 2 kg and 3 kg. The 3 kg fragment flies off at 12 m/s. Find the speed of the 2 kg fragment.
A ball is dropped from a height of 5 m onto a hard floor and bounces back up to a height of 1.25 m. Find the coefficient of restitution.
A 1 kg ball moving at 6 m/s collides head-on elastically with a stationary 2 kg ball. Find the velocity of each ball after the collision.
Stuck on a concept in Centre of Mass & Collisions?
Message Ajay Sir directly on WhatsApp for doubt support on this chapter.