Question Details

Consider the following two statements: 1. Linear momentum of a system of particles is zero 2. Kinetic energy of a system of particles is zero Then

Options

A

1 implies 2 and 2 implies 1

B

1 does not imply 2 and 2 does not imply

C

1 implies 2 but 2 does not imply 1

D

1 does not imply 2 but 2 implies 1

Correct Answer :

1 does not imply 2 but 2 implies 1

Solution :

The correct option is: 1 does not imply 2 but 2 implies 1

Let us analyze the two statements step-by-step to understand the logical relationship between them.

Statement 1: Linear momentum of a system of particles is zero.
The total linear momentum P of a system of n particles is the vector sum of the individual linear momenta of the particles:
P=p1+p2+...+pn=i=1nmivi
If the total linear momentum is zero (P=0), it means the vector sum of the individual momenta is zero. This does not require each individual velocity vi to be zero. For example, in a two-particle system, if one particle moves with velocity v and another identical particle moves with velocity -v, the total linear momentum is:
P=mv+m(-v)=0
However, since the particles are in motion, the total kinetic energy of the system is:
K=12mv2+12m(-v)2=mv20
Thus, Statement 1 does not imply Statement 2.

Statement 2: Kinetic energy of a system of particles is zero.
The total kinetic energy K of a system of particles is the sum of the individual kinetic energies:
K=i=1n12mivi2
Since mass mi is always positive and the term vi2 is non-negative, the kinetic energy of each particle is non-negative (Ki0). For the sum of non-negative terms to be zero, each individual term must be zero:
12mivi2=0vi=0
for all i. Since all particles are at rest, their individual linear momenta are also zero:
pi=mivi=0
Consequently, the total linear momentum of the system must be zero:
P=pi=0
Thus, Statement 2 implies Statement 1.

Therefore, Statement 1 does not imply Statement 2, but Statement 2 implies Statement 1.

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