Maximum height of a projectile thrown from a rooftop

[s.dyseman]

Homework Statement

A man stands on the roof of a building of height 14.6m and throws a rock with a velocity of magnitude 30.8m/s at an angle of 33.2∘ above the horizontal. You can ignore air resistance.

Calculate the maximum height above the roof reached by the rock.

Homework Equations

Velocity and position equations

Basic trigonometry

The Attempt at a Solution

Initially, I solved for the y-component of the velocity vector given: V=30.8*Sin(33.2)=16.86m/s

Then, I solved for the amount of time it would take for the rock to reach maximum height, where the velocity of the y-component vector is equal to 0: Vy=Voy+g*t=16.86-9.8t=1.72s

I plug this time into the position equation of Y=Yo+Voy*t+g*t^2=14.6+16.86(1.72)-4.9(1.72)^2=29.1m

So, the maximum height should be equal to 29.1m. Not sure why this is incorrect... Perhaps I calculated the vector incorrectly?

 

[mfb]

Calculate the maximum height above the roof reached by the rock.

You calculated the maximum height above the ground (and I can confirm this value).

 

[s.dyseman]

Ah, so I just needed to subtract the height of the roof... Simple detail I missed... Thank you!