Question

A force of 10N acts on a body of mass 2 kg for 2 sec. Rate of change of momentum of body is F A. 5kg m/secB. 10kg m/sec? C. 15kg m/sec D. none of these​

Answer 1

Step 1: Acceleration calculation

Applying Newton's second law

                ∑F=ma

                ⇒F=ma

                ⇒10(N)=20(kg) a

                ⇒a=0.5m/s2

Step 1: Final speed

Since acceleration is constant,

∴ Applying equation of motion

                   v=u+at

u= Initial speed =0

v= Final speed

                  v=0+0.5(m/s2)×10(s)

                     =5m/s

Step 2: Change in momentum ΔP

                ΔP=m(v−u)

                        =20(5−0)kgm/s

                        =100kgm/s

Hence option B is correct.

Alternate solution

Impulse J=Force×time

                  =10(N)10(S)

                  =100NS

Impulse J=ΔP 

          ΔP=100kgm/s

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