If a stationary firecracker explodes into the number of particles, then the centre of mass will:

CONCEPT:

Centre of mass:

• The centre of mass of a body or system of a particle is defined as, a point at which the whole of the mass of the body or all the masses of a system of particle appeared to be concentrated.

The motion of the centre of mass:

• Let there are n particles of masses m1, m2,..., mn.
• If all the masses are moving then,

⇒ Mv = m1v1 + m2v2 + ... + mnvn

⇒ Ma = m1a1 + m2a2 + ... + mnan

⇒ \(M\vec{a}=\vec{F_1}+\vec{F_2}+...+\vec{F_n}\)

⇒ M = m1 + m2 + ... + mn

• Thus, the total mass of a system of particles times the acceleration of its centre of mass is the vector sum of all the forces acting on the system of particles.
• The internal forces contribute nothing to the motion of the centre of mass.

EXPLANATION:

• In the given question a stationary firecracker explodes into a number of particles.
• When the firecracker explodes only internal forces acts on the firecracker and we know that the internal forces contribute nothing to the motion of the centre of mass.
• Therefore the centre of mass will remain stationary after the explosion. Hence, option 1 is correct.