size and direction of total momentum of two cars when collide?

Question

A 3900 kg truck traveling with a velocity of 11.5 m/s due north collides head-on with a 1450 kg car traveling with a velocity of 24 m/s due south. The two vehicles stick together after the collision.

What are the size and direction of the total momentum of the two vehicles after they collide?

Answer 1

Momentum is conserved, so the momentum before collision = momentum after.

Before momentum = 3900*11.5 - 1450*24 = 10050 kg*m/s North

After momentum is the same, (3900+1450)*v = 10050,

v = 1.88 m/s North

Answer 2

By law of conservation of momentum,
Total momentum before collision = Total momentum after collision
Initial momentum (truck)= 3900 kg x 11.5 m/s = 44850 Kg-m
Initial momentum (car) = 1450 Kg x (-24 m/s) = - 34800 Kg-m
Total Initial momentum = 10050 Kg-m due north
After head on collision, mass = 5350 Kg
By law of conservation of momentum,
the final momentum = 10050 Kg-m
The velocity = Final momentum / Combined mass
......... " .........= 10050 / 5350 = 1.879 m/s towards north
....................... .................. ......= ====================