# Velocity of image in plane mirror

## Homework Statement

A mirror is moving to the right with a velocity 15 m/s, and an object is moving to the right with a speed of 5m/s. All speeds are wrt ground. Find the velocity of image wrt ground.

## The Attempt at a Solution

I present to you two probable solutions:
1) Using formula: VIMAGE=2VMIRROR-VOBJECT
Now, its a mere substitution problem. Using right as positive direction, we get the required velocity as 25m/s to the right.
2) This is a controversial one. I thought about this as i like to explore all the different correct of incorrect methods of a problem.
the above problem is equivalent to: the mirror is moving to the right with a velocity of 10m/s and the object is at rest. Now, substituting in the formula used in the previous method, VIMAGE=20m/s to the right.

Now, my book says that that the correct answer is 10m/s, but its not matching with any of my answers. Please check it and let me know why both are incorrect.

#### Attachments

84 KB · Views: 559

CWatters
Homework Helper
Gold Member
You could try making two scale drawings, one showing the starting position of the object, mirror and image, and another showing their positions after say 1 second. Figure out how far the image moved in that time.

Yeah, i'll try by that method.

CWatters
Homework Helper
Gold Member
PS: Book answers are sometimes wrong.

CWatters
Homework Helper
Gold Member