# Homework help

1. Jan 30, 2006

### confused0229

im practically lost in physics and need some help. it would be greatly appreciated.

A ball is thrown upward from the top of a 25.6 m tall building. The ball's initial speed is 12 m/s. At the same instant, a person is running on the ground at a distance of 29.4 m from the building. What must be the average speed of the person if he is to catch the ball at the bottom of the building?

i am really lost in physics , and need some help. it would be greatly appreciated. thankyou

A ball is thrown upward from the top of a 25.6 m tall building. The ball's initial speed is 12 m/s. At the same instant, a person is running on the ground at a distance of 29.4 m from the building. What must be the average speed of the person if he is to catch the ball at the bottom of the building?

Last edited by a moderator: Jan 31, 2006
2. Jan 31, 2006

### Staff: Mentor

What are the equations that relate position, velocity and acceleration of an object? Use those equations to figure out how the ball moves with time as it goes up, stops at the top of its arc, and then accelerates down. These equations will let you figure out what time the ball will reach the bottom of the building. Then given the distance of the runner initially, you can figure out the speed needed to get the runner there at the same time. Too bad they didn't tell you how tall the runner is -- I guess you have to assume that they make a shoestring catch (catch the ball just as it reaches the ground).

3. Jan 31, 2006

### andrevdh

The elapsed time for the ball to reach the ground will be the same time for the catcher to cover the 29.4 meters (and then splat against the wall!).