Initial velocity of a Ball thrown up

[simpleee]

Can someone one show me a step by step example of how to work out a problem where a ball is thrown up and it is a catched after let's say 10.5s, so how would I find out the initial velocity?

 

[tiny-tim]

Welcome to PF!

Hi simpleee! Welcome to PF!

You have s t and a, and you want to find u …

which of the usual constant acceleration equations do you think will help here?

 

[simpleee]

truthfully, I am not quiet sure.
I need help understanding which one to use and why exactly I should use it.
s = ut + 1/2 at squared

 

[simpleee]

Oh and thank you for the welcome. =]

 

[tiny-tim]

truthfully, I am not quiet sure.
I need help understanding which one to use and why exactly I should use it.
s = ut + 1/2 at squared

(try using the X² tag just above the Reply box )

ok … there's only three constant acceleration equations, each with four variables, so you just chose the equation with the four variables that you're interested in.

In this case, you have s t and a, and you want to find u, so you choose s = ut + 1/2 at² because it has all of them.

 

[simpleee]

but i only have 10.5s and 9.8 for gravity.
So how would i know the rest?

 

[tiny-tim]

but i only have 10.5s and 9.8 for gravity.
So how would i know the rest?

u = 10.5, a = -9.8, and s = 0 (I'm assuming that the person catches it at the same height that (s)he throws it from ).

 

[simpleee]

0 = 10.5 t + 1/2 9.8 t²
0 = 10.5 - 4.9 t²

 

[tiny-tim]

0 = 10.5 t + 1/2 9.8 t²
0 = 10.5 - 4.9 t²

You mean 0 = 10.5 - 4.9 t …

yes, that's right. ​

 

[simpleee]

Do I get the t by itself now?
I think I might have posted this on the wrong section. .-.

 

[tiny-tim]

Do I get the t by itself now?

Yes … t = 10.5/4.9.

I think I might have posted this on the wrong section. .-.

That happens quite a lot here! ​

 

[simpleee]

Why did it turn into 10.5/4.9?
Is there any rules on how many times we can ask for help? o.o

 

[tiny-tim]

Why did it turn into 10.5/4.9?

0 = 10.5 t - 1/2 9.8 t²

so 0 = 10.5 - 4.9 t

so 10.5 = 4.9t

so t = 10.5/4.9

Is there any rules on how many times we can ask for help? o.o

You have to keep asking until you understand it!

 

[simpleee]

Good, good.
All the better! ^_^
2.1m/s?

 

[Sobeita]

I guess this problem depends on how strong your esophagus is.