A point mass of `1 kg` collides elastically with a stationary point mass of `5 kg`. After their collision, the `1kg`, mass reverses its direction and moves with a speed of `2ms^(-1)` . Which of the following statement(s) is (are) correct for the system of these two masses?

Options

A. Total momentum of the system is `3 kg ms^(-1)`
B. Momentum of 5 kg mass after collision is `4 kgm s^(-1)`
C. Kinetic energy of the centre of mass is 0.75 J
D. Total kinetic energy of the system is 4 J

Answer

A, C

Explanation

By conservation of linear momentum
`u = 5 v - 2 " " …..(i)`
By Newton’s experimental law of collision
`u = v + 2 " "…….(ii)`
Using Eqs. (i) and (ii), we have `v = 1m//s and u = 3m//s`
Kinetic energy of the centre of mass = `1/2 m_("system") v_(CM)^(2) = 0.75 J`