Final Velocity Calculation for Inelastic Collision of Freight Trains

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In a completely inelastic collision between two freight trains, the final velocity must be calculated using the conservation of momentum. The masses of Engine 1 and Engine 2 are 1.4x10^4 kg and 1.5x10^4 kg, respectively, with initial velocities of 45 km/h [N] and 53 km/h [W]. The user initially miscalculated the momentum by not dividing by the total mass after summing the momentum contributions. The correct final velocity, as per the textbook, is 9.7 m/s. Acknowledging the mistake in the calculation process is crucial for arriving at the correct answer.
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Homework Statement


Two freight trains have a completely inelastic collision at a track crossing. Engine 1 has a mass of 1.4x10^4 kg and is initially traveling at 45 km/h [N].
Engine 2 has a mass of 1.5x10^4 kg and is initially traveling at 53 km/h [W]. Calculate the final velocity.

Homework Equations

The Attempt at a Solution


p^2=p1^2+ p2^2
=(1.4x10^4)(12.5m/s)^2+ (1.5x10^4)(14.72m/s)^2
=281740m/s

The answer in the textbook is 9.7m/s. What am I doing wrong?
 
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I just realized my mistake, i forgot to divide it by both mass
 
Thread 'Correct statement about size of wire to produce larger extension'

Thread 'Correct statement about size of wire to produce larger extension'

The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...
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