Posted by Sandy on Sunday, September 12, 2010 at 8:51pm.
Two rocks are thrown off the edge of a cliff that is 15.0 m above the ground. The first rock is thrown upward, at a velocity of +12.0 m/s. The second is thrown downward, at a velocity of −12.0 m/s. Ignore air resistance.
Determine (a) how long it takes the first rock to hit the ground and (b) at what velocity it hits. Determine (c) how long it takes the second rock to hit the ground and (b) at what velocity it hits.

Physics  bobpursley, Sunday, September 12, 2010 at 8:56pm
Both are solved the same way:
Hf=hi+vi*t4.9t^2
put in hi (15), hf(zero), vi (either 12, or12), and solve for t.
velocity? Vf=Vi9.8t