IIT JEE , AIEEE Forum - Physics , Mechanics - a body approaching africtionless surface wit (4i-j) and rebounds wit(i+3j).wat's the 'e'

iamarijit

question on collisions

metal

Hi,

the question is not clear.

Do you mean that the body is approaching a frictionless wall with some initial velocity and rebounds with some final velocity???

feynmann

edited.

tanveergill

Feynmann is wrong
The answer is 9/16

The change in velocity due to collision is only in the direction perpendicular to direction of collision.

Hence we can find a vector perpendicular to surface of collision by finding change in velocity.

Change in velocity is found by subtracting the velocity vectors:

(4i - j) - (i + 3j) = 3i - 4j

This vector is perpendicular to surface.

velocity perpendicular to surface before the collision:

(4i - j).(3i - 4j)/5 = 16/5

velocity perpendicular to surface after the collision:

(i + 3j).(3i - 4j)/5 = -9/5

e = 9/5 * 5/16 = 9/16

elessar_iitkgp

Excellent reply @ tanveergill