Answer:

Explanation:
Assuming that cars 4 and 5 have same mass so that the momentum
P=mv where m is mass and v is velocity hence
Momentum=0+2mv+3mv=5mv
The final mass is 2m+3m=5m
From aw of conservation of momentum
hence 
Therefore, the speed is 
Well its C, cant show you the work its in my head sorry.
Answer:
Explanation:
Velocity of a wave is describe as
velocity =Frequency × Wavelength
Mathematically
v = fλ
Hence, Frequency, F = v / λ
Wavelength λ = v/f
So, if the frequency is kept constant, wavelength of the wave becomes directly proportional to velocity of the wave.
And this implies that, as the speed double, the wavelength is double.