Question

An electron moving at a speed of $ 5\times {{10}^{6}}m{{s}^{-1}} $ is shot through a sheet of paper which is $ 2.1\times {{10}^{-4}}cm $ thick. The electron emerges from the paper with speed of $ 2\times {{10}^{6}}m{{s}^{-1}}. $ The rime taken by the electron in a second to pass through the paper sheet is

• A. $ 5\times {{10}^{-12}} $
• B. $ 6\times {{10}^{-13}} $
• C. $ 3\times {{10}^{-12}} $
• D. $ 5\times {{10}^{-13}} $

Answer 1

Answer: (B)

(i) The collision is said to be elastic when the kinetic energy is conserved. (ii) Linear momentum is conserved in all types of collision (iii) Angular momentum of a system remain constant if resultant torque acting on it is equal to zero. As $ L=I\omega , $ so if $ \vec{\tau }=0 $ then $ I\omega =cons\tan t $ (iv) In all physical process the total energy is conserved. So, option is correct.