# What hits the ground first?

1. Dec 13, 2009

### Idrees

What hits the ground first??

1. The problem statement, all variables and given/known data

If we simultaneously throw two tennis balls horizontally from the top of a building, one at 10 m/s and the other at 14 m/s. Neglecting the air resistance, which one will hit the ground first???

2. Relevant equations
i dont think we use equations, but we have to consider the speed of each ball and how they are thrown horizontally??

3. The attempt at a solution

I think the ball with 10 m/s should hit the ground first because it wont reach far and eventually fall vertically from the top of buliding ?? please help out??

2. Dec 13, 2009

### Redd

Re: What hits the ground first??

Horizontal velocity does not affect vertical velocity.

3. Dec 14, 2009

### mg0stisha

Re: What hits the ground first??

You could also use equations of projectile motion to confirm this.

4. Dec 14, 2009

### mugaliens

Re: What hits the ground first??

Technically, the 10 m/s tennis ball will hit the ground first, but not for the reason you mentioned.

It's because the Earth is round! The ground where the 14 m/s tennis ball impacts is just a few microns lower, so that ball has further to fall!

Otherwise, assuming flat Earth, they'd both hit at the same time.

5. Dec 14, 2009

### modulus

Re: What hits the ground first??

Yes, considering the earth is flat, they both will hit at the same time.
The one with an initial speed of 10m/s will travel a less distance and the one with an initial velocity of 14m/s will travel more, but they will take the same time.
You can verify this with this equation:
For motion on the y-axis:- h=uyt - 1/2gt2

since 'uy' is zero, the equation simplifies to:-

h= -1/2gt2
or, t=sqrt of (2h/g)

Since 'h' and 'g' are same in the case of both the balls, the time taken by each to reach the ground will be equal.