Physics
posted by M .
Two objects A and B are involved in a totally elastic collision The mass of A is 8.8 kg and the mass of B is 0.5 kg. The velocity of A is 4.5 m/s and the velocity of B is 0 m/s. If they collide elastically, what will be the final velocity of A in m/s?

You have to use two equations:
conservation of momentum
a*Va+b*Vb=aVa'+bVb'
solve for Va'
Va'=(a*Va+b*VbbVb')/a
Now put that expression for va' into the conservation of momentum
1/2 aVa^2+1/2bVb^2=1/2a Va'^2 +1/2 b Vb'^2
and then start solving for Vb'
A bit of algebra will be required. Then go back an solve for Va' 
How exactly are you supposed to use the second equation to solve for Vb' if you don't know Va'^2?

m1=8.8 kg, v1=4.5 m/s
m2=0.5 kg, v2=0
u1=?
u1= (m1m2)v1/)m1+m2),
u2=2m1v1/(m1+m2). 
In the case of completely elastic collision, not only momentum is conserved but KE is also conserved. Considering these two principles, you get two equations from which you can find V1 and V2 in terms m1,m2 and U1.