- #1

benbaum

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## Homework Statement

A man stands on the roof of a 10.0 m -tall building and throws a rock with a velocity of magnitude 24.0 m/s at an angle of 30.0 degrees above the horizontal. You can ignore air resistance.

Calculate the magnitude of the velocity of the rock just before it strikes the ground

Calculate the horizontal distance from the base of the building to the point where the rock strikes the ground.

## Homework Equations

For Velocity:

Vy (final velocity)=V0y-gT where g is 9.8 <br>

V0y (initial Y)= v0sin(theta) = 12 (?) Where V0 is initial velocity

time in flight (usable?) = 2V0y/G =2.45?

For range Delta X=Vx * T where V0x=V0Cos(theta)

Vfinal= square root of(vy^2 + vx^2)

## The Attempt at a Solution

I think my real problem might be I'm not using the right equations.

Anyway, my approach was to get the two components of my final velocity by getting Vy and Vx and then use the Pythagorean theorem to get the final velocity. Initial velocity of Y and X component were easy, I plugged the given values into them and got 20.78 for V0x= V0cos(theta) and 12 for V0y=V0sin(theta). Since the initial velocity of X component is constant, I set out to solve for the rest of the final velocity for the Y component.

The first equation I used was the "time in flight" equation, which I'm not sure if it works in one of these types of problems, since it is from a height. When solving that equation I got 2.45 for T and plugged it into the final y velocity equation Vy =12-9.8*2.45 =-12.01.

Finally, I used the "Vfinal" equation square root of(20.78^2+-12.01^2) = 24.001m/s which is apparently wrong.

What am I doing wrong?