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Class 9

Chapter 9 Class 9 - Force and Laws Of Motion

Last updated at May 29, 2023 by Teachoo

NCERT Question 11 Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m sā1 before the collision during which they stick together. What will be the velocity of the combined object after collision? Mass of object 1 = š_1 = 1.5 kg Mass of object 2 = š_2 = 1.5 kg Velocity of object 1 = u1 = 2.5 m/s Velocity of object 2 = u2 = ā 2.5 m/s Note: u2 is negative since it is in opposite direction of u1 After collision, the objects stick together ā“ Combined mass = m1 + m2 = 1.5 + 1.5 = 3 kg Velocity of combined object = v Finding momentum before and after collision Momentum before Momentum = Momentum of Object 1 + Momentum of Object 2 = 1.5 Ć 2.5 + 1.5 Ć (ā2.5) = 1.5 Ć 2.5 ā 1.5 Ć 2.5 = 0 Momentum after Momentum = Total Mass Ć Velocity After = 3 Ć v = 3v Momentum after Momentum = Total Mass Ć Velocity After = 3 Ć v = 3v According to law of conservation of momentum, Total momentum before collision = Total momentum after collision 0 = 3v v = 0/3 v = 0 m/s