# Mass and free fall question

1. Feb 7, 2008

### tengtou

A ball of mass .5 kg is dropped from a height of 5 m. What is the greatest velocity it will have just before hitting the ground?

vf squared = vi squared + 2ad

vf squared = 0 squared + 2(9.8)(5)

vf = 9.8 m/s

So the greatest velocity is 9.8 m/s, right?

I am still very confuzzled and I think this is the right answer because where did the mass go? Or it doesn't even matter? Can someone verify?

Thanks!

2. Feb 7, 2008

### rl.bhat

Yes. Mass does not matter in the free fall under gravity. All the body get accelerated equally.

3. Feb 7, 2008

### Dick

Welcome to the forums! No, mass doesn't matter. The acceleration downwards is g, independent of mass, ask Galileo. It's a purely kinematical problem.

4. Feb 7, 2008

### tengtou

Thanks! So is my answer correct?

5. Feb 7, 2008

### Dick

Approximately, yes. I would round the answer to 9.9m/sec. But that's a detail.

6. Feb 7, 2008

### tengtou

Sweet! Thanks!

7. Feb 7, 2008

### tengtou

I don't know why the question had mass in it. Trick question or something haha.

8. Feb 7, 2008

### Dick

In real world problems YOU have to figure out what's important and what isn't. It's just practice.