Question

can momentum be conserved for a system if there are external forces acting on the system ? if so , under what conditions ? if not , why ?

Answer 1

Answer:

No. The law of conservation of momentum holds only when external force(s) acting on the body is 0.

Explanation:

Consider a body with no external forces, so,

∑F(ext) = 0

∴ From Newton's 2nd Law of motion,

∑F(all forces acting on body) = ma = Δp/Δt

So,Δp/Δt =0

⇒Δp=0

⇒p(final) =p(initial)

Hence momentum remains conserved.