Question

Two rockets of rest length L approach each other with equal speeds of 0.4c. How
long would one rocket appear to the other?

Answer 1

Since both rockets move at the speed comparable to the speed of light, one rocket will notice that the length of the other will decrease following Lorentz transformation:

$$L_c=L\sqrt{1-v^2/c^2}=\\=L\sqrt{1-(0.4c)^2/c^2}=0.917L.$$