elastic collision

[drkidd22]

One ball traveling at 17.7 m/s strikes a second ball at rest in an elastic collision. If the mass of the first ball is 30 kg and the mass of the second is 1.2 kg, to the nearest tenth of a m/s what is the velocity of the first ball after the collision?

2. Relevant equations

http://img.sparknotes.com/content/testprep/bookimgs/sat2/physics/0001/12m1v1.gif

[ApexOfDE]

you need a 2nd eq, conservation of momentum.