# Homework Help: Ball thrown from top of building

1. Jul 16, 2008

### jhoffma4

rock is thrown from the edge of the top of a 100-ft tall building at some unknown angle above the horizontal. The rock strikes the ground a horizontal distance of 160 ft from the base of the building 5.0 s after being thrown. Assume that the ground is level and that the side of the building is vertical. Determine the speed with which the rock was thrown.

I found the x component of the initial velocity to be 32m/s and I think I need to find the y(max). I found t(max) for height to be v(0)/g (for the y component). And y(tmax)=h+1/2(v(o)/g), but this information does not seem to help me any.

Help?

2. Jul 17, 2008

### alphysicist

Hi jhoffma4,

Be careful with your units; this will be 32 ft/s.

This equation does not look correct to me.

I would not worry about the maximum height. You know the vertical displacement at a particular time after launch, right? That's all you need to find the initial vertical velocity. What do you get?