# WBJEE: Important Questions and Preparation Tips – Centre of Mass

Students can’t miss any single topic of any subject if they want to get selected in **WBJEE** Examination 2018. But it is not possible for stduents to revise the complete theory before the examination. To tackle this problem students will have to make notes which should consists of all important concepts, formulae and previous year solved questions. The study of previous year questions helps us to understand the difficulty level of the questions asked in previous year WBJEE Examination. In this article we bring to you the complete chapter notes of chapter **Centre of Mass** including topics like the **centre of mass of two points system, centre of mass of n points system, impulse, thrust** etc. These chapter notes are prepared by Subject Expert and are based on the latest syllabus of WBJEE Examination. These notes are in very concise form and can be used for quick revision before the examination.

**About the exam:**

West Bengal Joint Entrance Examination (WBJEE) is a state level common entrance test organized by West Bengal Joint Entrance Examinations Board for admission to the Undergraduate Level Engineering and Medical Courses through a common entrance test in the State of West Bengal.

**Important Concepts:**

**Important Questions and Preparation Tips – Work Power and Energy**

**Some important solved questions are given below:**

**Question 1:**

A large number of particles are placed around the origin, each at a distance R from the origin. The distance of the center of mass of the system from the origin is

(A) = R (B) ≤ R

(C) > R (D) ≥ R

**Solution 1:**

**Correct Option: (B)**

If OAB is a sector of a circle, radius r, with angle 2α at the centre then the centre of mass lies on line of symmetry such that,

If, arc AB tends to zero then the centre of mass is at distance R from the origin. And as the arc length AB increases, centre of mass starts moving down.

**Important Questions and Preparation Tips – Laws of Motion**

**Question 2:**

Two bodies of masses *m*_{1} and *m*_{2} are separated by a distance R. The distance of the centre of mass of the bodies from the mass *m*_{1} is

**Solution 2:**

**Important Questions and Preparation Tips - Thermodynamics**

**Question 3:**

Distance of the centre of mass of a solid uniform cone from its vertex is *z*_{}. If the radius of its base is *R* and its height is *h* then *z*_{} is equal to

**Solution 3:**

**Correct Option: (A)**

**Question 4:**

**Solution 4:**

**Correct Option: (B)**