In: Physics
A body of mass 2.1 kg makes an elastic collision with another body at rest and continues to move in the original direction but with 1/6 of its original speed. (a) What is the mass of the other body? (b) What is the speed of the two-body center of mass if the initial speed of the 2.1 kg body was 3.1 m/s?
Let particles 1 and 2 have masses m1, m2, and velocities u1, u2 before collision, v1, v2 after collision.
By conservation of momentum before and after the collision
By the conservation of the kinetic energy
These equations may be solved directly to find
m1 = 2.1 kg, v1 = 1/6 u1, u2 = 0
from first equation
(b) If there is no external force on the system then the motion of the center of mass of the system remains unchanged,
The velocity of com of two bodies before collision = (m1u1 + m2u2)/(m1+m2)
= (2.1 x 3.1 + 1,5 x0 ) / (2.1+1.5)
= 1.8 m/s
There is no external force, hence the velocity of the center of mass will remain same after Collison i.e. 1.8 m/s