From the question,
[tex]u = 0m {s}^{ - 1}[/tex]
[tex]v = 6m {s}^{ - 1} [/tex]
[tex]t = 3s[/tex]
[tex]F=12N [/tex]
Using Impulse, the product of the constant force, F and time t equals the product of the mass of the body and change in velocity.
[tex]Ft =m(v-u) [/tex]
[tex]12(3.0)=m(6.0- \: 0)[/tex]
This implies that
[tex]36.0 = 6m[/tex]
[tex]m = \frac{36.0}{6.0} [/tex]
[tex] \therefore \: m = 6.0kg[/tex]
You can also use the equation of linear motion,
[tex]v = u + at[/tex]
[tex]6 = 0 + a(3)[/tex]
[tex]6 = 3a[/tex]
[tex]a = \frac{6}{3} [/tex]
[tex]a = 2 {ms}^{ - 2} [/tex]
But
[tex]F=ma [/tex]
[tex]12 = m(2)[/tex]
[tex]12 = 2m[/tex]
[tex] \frac{12}{2} = m[/tex]
[tex] \therefore \: m = 6kg[/tex]
