1st TIME ON INTERNET: COOL METHOD TO FIND THE VELOCITY OF BULLET

On internet you can find many websites (http://www.youtube.com/watch?v=Lkuo6nZ6nZM) describing the method of pendulum to find the velocity of bullet. Here they use the concept of momentum conservation. But this method is not the perfect one as you need accurate measurement of length and heights to measure the velocity. In some websites you may find the use of moving drum camera .........

In this article i have described a method using circular motion to find the velocity of bullet which is simple and error free.

Look at the fig to understand the apparatus required to find the velocity::

CLICK TO GET A MAGNIFIED VIEW

The speed of the bullet can be determined by allowing the bullet to pass through two rotating paper discs mounted at a distance "d" apart on the axle. the angular velocity of axle is know and the value is "ω". 

Then fire the bullet. The bullet first makes a hole in the first disc at "A" ( see fig.). Then moving a distance "d" it again makes a hole at point "B" in the second disc. Time taken by the bullet in moving a distance "d" is given by:

T=d/v  -------(i)

where v is the velocity of bullet

Now there is a angular displacement "Ѳ" between the two discs as the second disc has rotated through an angle Ѳ in the same time interval "T" and T is also given by 

T=Ѳ/ω --------(ii)

from eq. (i) and (ii) it is clear that 

T=Ѳ/ω=d/v

SOLVING:

v=dω/Ѳ

d,Ѳ,ω are known so velocity "v" can be calculated .

NOTE:

ω should not be very large or very small

disc should be made of paper and of large radius

paper disc is used so that the bullet's momentum remains constant

SOURCE: 

MECHANICS FOR IIT-JEE VOL-1, by ER ANURAG MISHRA