# Throwing a dart from a roof - Velocity

1. May 8, 2010

### mybrohshi5

1. The problem statement, all variables and given/known data

A dart is thrown horizontally from a buildings rooftop. The dart's time of flight is 2.0 s. The dart sticks in the ground such that it makes a 53.1 degree angle with the ground.

With what speed was the dart thrown?

3. The attempt at a solution

I am studying for my final and i do not get this problem from one of my previous tests.

The answer is 14.7 m/s and i have no idea how to get it. Can anyone point me in the right direction.

Thank you :)

2. May 8, 2010

### rock.freak667

Well if it is throw horizontally, then the initial vertical velocity is zero right? Using an equation of motion, what would be final vertical velocity when t=2?

3. May 8, 2010

### mybrohshi5

Is the final vertical velocity when t=2 just 19.6 m/s

I got that from

Vf = Vi + at

oh so then from that the x component of the Vf will be the same as the velocity initial correct?

so

tan(53.1) = 19.6 / Vfx

Vfx = 14.7 m/s

Does that seem right?

4. May 8, 2010

### rock.freak667

Yes that looks correct.

5. May 8, 2010

### mybrohshi5

Yay! thank you very much :)