First, find the magnitude of v , that is, the speed v of the two-car unit after the collision.?
in this problem we will consider the collision of two cars initially moving at right angles. we assume that after the collision the cars stick together and travel off as a single unit. the collision is therefore completely inelastic.

two cars of masses m1 and m2 collide at an intersection. before the collision, car 1 was traveling eastward at a speed of v1, and car 2 was traveling northward at a speed of v2. (figure 1) after the collision, the two cars stick together and travel off in the direction shown.

first, find the magnitude of v , that is, the speed v of the two-car unit after the collision.

express v in terms of m1, m2, and the cars' initial speeds v1 and v2.
i got an answer to be v=sqrooot( (m1*v1)/(m1+m2))^2+((m2*v2)/(m1+m2) )^2
is this wrong ? ?