A railway truck with a mass of 6,000 kg rolling at 4 m/s collides with a stationary truck of mass 10,000 kg. The trucks join together. At what speed do they move after the
collision?

Inelastic collision formula is used when the objects stick together after collision. Use elastic formula if they move at separate speeds

i think it because equal matrices have equal dimensions, only square matrices can be symmetric. for all indices and . every square diagonal matrix is symmetric, since all off-diagonal elements are zero. in linear algebra, a real symmetric matrix represents a self-adjoint operator over a real inner product space.