A point mass of 1kg 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 statements (s) is (are) correct for the system of these two masses?

Options

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

Answer

A, C

Explanation

(a,c)
According to law of conservation of linear momentum
`1xxu_1+5xx0=1(-2)+5(v_2)`
`rArr u_1=-2+5v_2….(i)`
The coefficient of restitution
`e=(v_2-v_1)/(u_1-u_2) rArr 1=(v_2-(-2))/(u_1-0)`
`rArr u_1=v_2+2….(ii)`
On solving (i) & (ii) we get desired results.