Question

An object is initially at a distance of $100cm$ from a plane mirro. If the mirror approaches the object at a speed of $5cm/sec$, then after $6sec$ the distance between the object and its image will be

• A. $60cm$
• B. $140cm$
• C. $170cm$
• D. $150cm$

Answer 1

The correct option is B $140cm$

Given that,

The distance of object from plane mirror $D=100cm$

So, initial distance of image and object

$=100-(-100)$

$=200cm$

Now, object approaches the mirror with the speed$v=5cm/s$

So, distance travelled by object in 6 sec

$D=5\times 6$

$D=30cm$

At this instant,

Distance between mirror and object

$D=100-30$

$D=70cm$

Now, the distance between image and object is

$D=70-(-70)$

$D=140cm$

Hence, the distance between the object and its image is $140cm$