When the position vector. r ⃗ \vec{r} r = xî + yĵ + zk̂ changes sign as - r ⃗ \vec{r} r , which one of the following vector will not flip under sign change ?

Question

G1 Physics · Accepted Answer

Under spatial inversion, r⃗ → -r⃗. Velocity is v⃗ = dr⃗/dt, so v⃗ → -v⃗. Therefore linear momentum p⃗ = mv⃗ also changes sign. Acceleration is a⃗ = dv⃗/dt, so under the same inversion it also changes sign. Angular momentum is L⃗ = r⃗ × p⃗. Under inversion, r⃗ → -r⃗ and p⃗ → -p⃗. Hence, L⃗ → (-r⃗)×(-p⃗) = r⃗×p⃗ = L⃗. Thus angular momentum does not flip. Correct option: D.