Question

NCERT CLASS IX - Science Textbook
Chapter 9 - Force and Laws of Motion

Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s - '1and 1 m s - '1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s - '1. Determine the velocity of the second object.

Answer 1

according to the law of conservation of momentum, m1u1+m2u2 =m1v1+m2v2

here, m1 = 100g =0.1kg
         m2= 200kg=0.2kg

u1 =2m/s
u2 =1m/s

         v1=1.67m/s
         v2= ?

thus, .1*2+ .2*1 = .1*1.67 + .2*v2
.2+0.2 =0.167 + 0.2 v2
.2 v2 = .2+.2 -0.167
hence,v2 = (0.4 - 0.167) /0.2 = 1.165 m/s

Answer 2

we know that  v2 = 2m1v1/m1+m2
Vfinal of other object is = 2×0.1×1..67/0.3
=1.11 so final velocity of second body will be 1.11 m/s