Question

A force 2i+j-k newtons acts on a body which is initially at rest. At the end of the 20 seconds, the velocity of the body is 4i+2j-2k m /s. What is the mass of the body.

Answer 1

For Motion along X axis :
4 = u + at
u=0, t=20
4=20a
a(x) =1/5 =0.2
But force =2 N
2=ma
m=10Kg.
Considering motion along any axis is sufficient. This case x axis.