Question

A plane mirror approaches a stationary person with acceleration $10m{s}^{-2}$. The acceleration of his image as seen by the person, will be

• A. $10m/s^2$
• B. $20m/s^2$
• C. $5m/s^2$
• D. $\text{can't determined}$

Answer 1

Answer: (B)

$20m/s^2$

If the acceleration of the person is a, the acceleration of the image will be -a (negative sign is to indicate that it is in the opposite direction)
So the acceleration of the image as seen by the person is the relative acceleration of the image and the person.
relative acceleration $=a-(-a)=2a$

in this case $a=10m{s}^{-2}$

acceleration of his image as seen by the person $20m{s}^{-2}$