Question

A driver is reversing his van at a speed of 3 m/s, The driver sees in his rear view mirror (plane mirror) the image of a bus parked behind his van. The speed at which the image of the bus appears to approach the driver is

• A. 6 m/s
• B. 4 m/s
• C. 3 m/s
• D. 2 m/s

Answer 1

Answer: (A)

6 m/s

The rear view mirror is a plane mirror.

In a plane mirror, object distance and image distance are always equal.

Now, the van is reversing at $3m/s$.

So, in $1s$, the van approaches the bus by $3m$.

Let the initial distance between the mirror and the bus be $xm$.

So, initial distance between the mirror and the image is $xm$.

Now, after $1s$, the mirror is at a distance of $(x-3)m$ from the bus.

The image is now $(x-3)m$ behind the mirror.

So, from its initial position, the image has moved by a distance $=x+3-(x-3)m=6m$.

The image has covered the distance of $6m$ in $1s$.

The image of the bus appears to approach the driver at a speed of $6m/s$.