# How do I find the direction of impulse vector in a collision?

I know that impulse is the change in linear momentum. Is the direction of impulse always along the change in momentum vector? Please explain.

You have already said you are aware that the impulse $$\mathbf J$$ is the change in linear momentum $$\Delta\mathbf p$$, so we have $$\mathbf J\equiv\Delta\mathbf p$$
In general, if we have two vectors $$\mathbf a$$ and $$\mathbf b$$ that are equal, then their components must be equal (let's assume we are working with 2D vectors here) $$a_x=b_x$$ $$a_y=b_y$$
So looking at the magnitude of $$\mathbf a$$: $$||\mathbf a||=\sqrt{a_x^2+a_y^2}=\sqrt{b_x^2+b_y^2}=||\mathbf b||$$
And looking at the direction of $$\mathbf a$$: $$\theta_a=\tan^{-1}\left(\frac{a_y}{a_x}\right)=\tan^{-1}\left(\frac{b_y}{b_x}\right)=\theta_b$$