Q.

Two particles of masses m1 and m2 in projectile motion have velocities v→1 and v→2 respectively at time t=0. They collide at time t0. Their velocities become v→1' and v→2' at time 2t0 while still moving in air. The value of |(m1v→1'+m2v→2')-(m1v→1+m2v→2)| is                  [2001]

1 zero  
2 (m1+m2)gt0  
3 12(m1+m2)gt0  
4 2(m1+m2)gt0  

Ans.

(4)

Fext=(m1+m2)g  and  Δt=2t0

Fext=ΔpΔt

∴  Δp=Fext Δt =(m1v→1'+m2v→2')-(m1v→1+m2v→2)

        =(m1+m2)g×2t0