Velocity of Image with Respect to Ground
Given:
• Velocity of object with respect to mirror:
V⃗OM = −î + 2ĵ + k̂
• Velocity of mirror with respect to ground:
V⃗M G = î + ĵ + k̂
• Normal vector of the mirror:
−î − ĵ
⃗n = −î − ĵ ⇒ n̂ = √
2
Step 1: Image velocity w.r.t mirror
For a plane mirror, the velocity of the image with respect to the mirror is given by:
V⃗IM = V⃗OM − 2(V⃗OM · n̂)n̂
Compute the dot product:
!
−î − ĵ −1 − 2 −3
V⃗OM · n̂ = (−î + 2ĵ + k̂) · √ = √ =√
2 2 2
Now compute:
!
−3 −î − ĵ
V⃗IM = (−î + 2ĵ + k̂) − 2 · √ · √ = (−î + 2ĵ + k̂) − 3(î + ĵ)
2 2
⇒ V⃗IM = −4î − ĵ + k̂
Step 2: Image velocity w.r.t ground
V⃗IG = V⃗IM + V⃗M G = (−4î − ĵ + k̂) + (î + ĵ + k̂) = −3î + 2k̂
Final Answer:
V⃗IG = −3î + 2k̂