Two automobiles, each of mass 1000 kg, are moving at the same speed, 20 m/s, when they collide and stick together. In what direction and at what speed does the wreckage move (a) if one car was driving north and one south (b) if one car was driving north and one east? A. The wreckage after collision is moving at the speed 18 m/s to the south.
B. The wreckage after collision is moving at the speed 9.0 m/s to the north.
C. The wreckage after collision is moving at the speed 9.0 m/s to the south.
D. The wreckage after collision is moving at the speed 18 m/s to the north.
E. The wreckage after collision is motionless.

The reckage after collision is motionless (E)

Explanation:

The first law of thermodynamics states that energy is neither created nor destroyed but is converted from one form to another.

The kind of collision described in the question above is known as a perfectly inelastic collision, and in this type of collision, the maximum kinetic energy is lost because the objects moving in opposite directions have a resultant momentum that is equal, but in opposite directions hence they cancel each other out.

The calculation is as follows:

m₁v₁ + m₂v₂

where:

m₁ = m₂ = 1000kg

v₁ = 20 m/s

v₂ = -20 m/s ( in the opposite vector direction)

∴ resultant momentum = (1000 × 20) + (1000 × -20)

= 20000 - 20000 = 0

∴ The reckage after collision is motionless