# Easy kinematics problem

• Dec 4th 2012, 02:38 PM
Cesc1
Easy kinematics problem
Hi! I'm dealing with this problem that seems to be very easy, however the teacher says I'm wrong, and I don't know where's my mistake (She didn't tell me). So I hope you can tell me where did I go wrong(Wink) Here's the problem:

A falling sky diver travels 64m in 2 seconds. How much will he travel in 8 seconds? (Ignore the air resistance)

My solution:

I used the equation y=yo+vot+1/2gt^2
with

y=64m
y0=0m
g=9.8 m/s^2
t=2s

Then I solved it for vo, obtaining vo=22.2 m/s. And finally obtained:

y=(22.2)(8)+1/2g(8)
^2=491.2 m

I don't know what did I do wrong, and the teacher didn't even tell me what was the right answer
(Wondering). I hope you guys help me figure it out. Thanks!
• Dec 8th 2012, 02:55 AM
puresoul
Re: Easy kinematics problem
Quote:

Originally Posted by Cesc1
Hi! I'm dealing with this problem that seems to be very easy, however the teacher says I'm wrong, and I don't know where's my mistake (She didn't tell me). So I hope you can tell me where did I go wrong(Wink) Here's the problem:

A falling sky diver travels 64m in 2 seconds. How much will he travel in 8 seconds? (Ignore the air resistance)

My solution:

I used the equation y=yo+vot+1/2gt^2
with

y=64m
y0=0m
g=9.8 m/s^2
t=2s

Then I solved it for vo, obtaining vo=22.2 m/s. And finally obtained:

y=(22.2)(8)+1/2g(8)
^2=491.2 m

I don't know what did I do wrong, and the teacher didn't even tell me what was the right answer
(Wondering). I hope you guys help me figure it out. Thanks!

What I understand from the question is that the diver has traveled in 2 seconds 64m then for another 8 seconds how much will he travel..

So we can find his velocity after 2 seconds and then use it to find the distance he traveled in 8s..

What you did is that u found his velocity when he just started travelling the 64 m..
After that you need to find the velocity that he was traveling with after 2 seconds and substitute that in the second equation-which you used to find the distance..
• Dec 11th 2012, 02:34 PM
Cesc1
Re: Easy kinematics problem
Quote:

Originally Posted by puresoul
What I understand from the question is that the diver has traveled in 2 seconds 64m then for another 8 seconds how much will he travel..

So we can find his velocity after 2 seconds and then use it to find the distance he traveled in 8s..

What you did is that u found his velocity when he just started travelling the 64 m..
After that you need to find the velocity that he was traveling with after 2 seconds and substitute that in the second equation-which you used to find the distance..

That's exactly what I had to do. Thanks!