Two Balls Dropped: Same Time Impact?

[Toranc3]

Homework Statement

A ball is thrown straight up from the edge of the roof of a building. A second ball is dropped from the roof 1 second later. You may ignore air resistance

If the height of the building is 20m what must the nitial speed of the first ball be if both are to hit the ground at the same time?

Homework Equations

y=yo+vo*t+1/2*a*t^(2)

The Attempt at a Solution

I had a question about the wording. So does the first two sentences mean that the first ball is thrown and when it travels for one second the second ball is about to drop? Or the first ball is thrown for some time t that is unknown and then one second after some time t the second ball is about to drop?
Thanks!

 

[Doc Al]

I had a question about the wording. So does the first two sentences mean that the first ball is thrown and when it travels for one second the second ball is about to drop?

Yes. At time t = 0 the first ball is thrown. At time t = 1 the second ball is dropped.

Or the first ball is thrown for some time t that is unknown and then one second after some time t the second ball is about to drop?

No.

 

[Toranc3]

Thank you!