Question

An object is approaching a fixed plane mirror with speed $15m{s}^{-1}$ making an angle of ${135}^o$ with the normal to the mirror. The speed of image w.r.t mirror is:

• A. $15m{s}^{-1}$
• B. $\frac{15}{\sqrt{2}}m{s}^{-1}$
• C. $15\sqrt{2}m{s}^{-1}$
• D. $30m{s}^{-1}$

Answer 1

Answer: (A)

$15m{s}^{-1}$

For a mirror, position of image from mirror is negative of position of object from mirror. This means $x=-x^{\prime }$

Therefore$\frac{dx}{dt}=-\frac{d{x}^{\prime }}{dt}$

But the velocity in y direction remains the same. Hence the magnitude of velocity remains the same as of object.