8 m/s
Explanation:
Using conservation of momentum :-
[tex]m1u1 + m2v1 = m1u2 + m2v2[/tex]
Where:
m1 = Mass of first vehicle
m2 = Mass of second vehicle
u1 = initial speed of first vehicle
v1 = initial speed of second vehicle
u2 = Final speed of first vehicle
v1 = Final speed of second vehicle
From the received informations:
[tex]m1 = m2[/tex]
[tex]v1 = 0[/tex]
[tex]v2 = u2 = 4 \frac{m}{s} [/tex]
So
[tex]m1u1 + 0 = 4m1 + 4m1[/tex]
Now divide both sides by m1 :-
[tex]u1 = 4 + 4[/tex]
[tex]u1 = 8m/s[/tex]
Therefore, final answer is 8 m/s