Grigoriy S. answered 12/04/21
AP Physics / Math Expert Teacher With 40 Years of Proven Success
If I understood the problem in a right way, after the collision two carts moved with the same speed
v = 0.9 m/s. It means this is inelastic collision and then we can write the law of conservation of linear momentum as
m1v1 + m2v2 =( m1 + m2)v ,
here
m1v1 - linear momentum of the first body before the collision,
m2v2 - linear momentum of the second body before the collision
( m1 + m2)v - linear momentum of the 2 bodies after the collision
From this equation the momentum of the first body
p1 = ( m1 + m2)v - m2v2
Just put in this equation all known values and you are done!