Tom walked 450 m south he then turned and walked 150 m to the north in 600 seconds what was his velocity

Velocity = displacement / time
Here, displacement = 450 - 150 = 300 m towards south
t = 600 s

Substitute their values, 
v = 300/600
v = 0.5 m/s towards south

Hope this helps!

Two cars collide, lock bumpers and move together after the collision.this collision is known as perfectly inelastic collision.