# Motion on a plane

1. May 26, 2009

### mohammed1992

Question:
A stone is throws with an initial horizontal velocity of 10m/s form the top of a tower 200m high.
a)where is the stone 2 seconds after being thrown?
b)when will it hit the ground?
c)what is the speed upon hitting the ground?

(this is not my homework it a question that wasn't discussed in class and i am not able to answer it)

2. May 26, 2009

### mohammed1992

Re: motion on a plane 2

Thank you

3. May 26, 2009

### mikelepore

The trick is that the x and y motions are independent and are superimposed on each other (an approximation good for the world being flat). If it is thrown horizontally, then the initial velocity has no y component. First, solve a problem as thought there is only y-motion, that it, a stone dropped vertically from rest. Find the time to hit the ground, the position at 2 seconds, and the final speed just before it hits the ground. Then do another problem as if there is only x-motion, as if it were sliding on a table. Neglecting air resistance, x-motion has a constant horizontal velocity, because gravity doesn't affect the x-motion. Find the position at 2 seconds. Find the x-velocity at the time when the first part of the problem, the y-solution, said it will hit the ground. Now you can combine the x-results and the y-results to get the things they ask for.

Last edited: May 26, 2009