Question

A force of 10 N is acting on a body of mass 20 kg for 10 seconds . Find change in its momentum .

Answer 1

change in momentum(Δp) = 1 N/sec
 HOW ???
F= mass(m) x acceleration(a)
Velocity(v)= Δa/Δt

So, applying F=ma, we get a=1/2...
Now, we know Momentum(p) = mv = m. (Δa/Δt) 
By putting values we will get Δp = mΔv= 20 x5 = 100 N/sec

Answer 2

Force = mass × acceleration.
         = mass × change in velocity/time      
     10 = 20 × change in velocity/ 10
⇒ change in velocity = 10 × 10 / 20
                               = 5 m/s
Change in momentum = mass × change in velocity
                                 = 20 × 5
                                 = 100 kg.m/s