physics question below, please help

Question

A car of mass 1 tonne travelling at 50km/h crashes into a stationary car of mass 2 tonnes on an icy road.
Neglecting any frictional forces and assuming that after the initial collision the cars are firmly bound together, use the principle of the conservation of momentum to determine the speed of the combined cars immediately after impact.

Answer 1

Before collision:

 

p_i = m₁v₁ + m₂(0) = m₁v₁

 

After collision:

 

p_f = (m₁ + m₂)v_f

 

Conservation of linear momentum:

 

p_i = p_f

 

m₁v₁ = (m₁ + m₂)v_f

 

v_f = [m₁/(m₁ + m₂)] v₁

 

Now plug in the values:

 

m₁ = 1 tonne

m₂ = 2 tonnes

v₁ = 50 km/h

 

You should be able to finish from here.