# Another mechanics question (a simpler one, I proimise!)

1. Nov 5, 2008

Another mechanics question :) (a simpler one, I proimise!)

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

http://img223.imageshack.us/img223/5172/112mz7.th.jpg [Broken]http://g.imageshack.us/thpix.php [Broken]
As the picture shows:
M=4kg
V0=5 m/s
h=5m
F(wind)=2N
angle=15 degrees

I need to find the distance on axis x of the ball when he hits the ground.

2. The attempt at a solution

So this is how I tried to solve it..

1. I'll try to calculate the distance the ball made untill he got back to the height he started with (the ball goes up a few metters, gets to a point where his speed its 0 and then drops down untill he hits the ground)

-Mg - F=Ma -> -40-2=4a -> a=-10.5 m/s2 (right?)

y=yo+v0t+0.5at2
0=0+5sin15t+0.5*(-10.5)*t2
-5.25t2+1.3t=0
t=0.247s

so to that point the ball made a progress on axis x:
X1=v*t=5cos15*0.247=1.19m

Now I need to find his progress on axis x from that point, when he got back to the original height he started with and is falling down 5m.
The speed on axis y is 5sin15 m/s, so the time it will take the ball to hit the ground from that point is:
-5=0-5sin15*t+0.5*(-10.5)*t2 (did I get all the minuses right?:shy:)
5.25t2+1.3t-5=0
t=0.86s

so on axis X...
X2=v*t=5cos15*0.86=4.15m

and alltogher..
X1+X2=5.35m

is there any mistake you can tell I made alond the way?

Last edited by a moderator: May 3, 2017
2. Nov 5, 2008

### heth

Re: Another mechanics question :) (a simpler one, I proimise!)

To check your answer, try doing the problem "all at once" rather than splitting it into two parts. If you get the same answer, it's probably right.

3. Nov 5, 2008

Re: Another mechanics question :) (a simpler one, I proimise!)

thanks heth.
btw, why cant I edit the title? pepole might get the impression that I'm dyslexic.

4. Nov 5, 2008

### Hootenanny

Staff Emeritus
Re: Another mechanics question :) (a simpler one, I proimise!)

You can edit your posts for a maximum of one hour after they were posted.

5. Nov 5, 2008

Re: Another mechanics question :) (a simpler one, I proimise!)

My approach about spelling is you cant criticize someone untill you try and write in his language.
And trust me, hebrew is not an easy one to learn..

BTW
Its kind of a weird question but are there by any chance people who know Hindi in PF? I'm looking for someone who can translate a few lines from english to Hindi for me :)

Last edited: Nov 5, 2008
6. Nov 5, 2008

### physics girl phd

Re: Another mechanics question :) (a simpler one, I proimise!)

Hi again! You might try to post this request in GD (general discussion)? Or look for someone who hints they may be from a country where Hindi is more dominant, and then send them a private message.

I'll confess to being fluent in only my native tongue, with a small working vocab in just a few romance languages.... mainly to make my kids laugh. I really need to buckle down and get some language-on-tape sets. It would be good to learn more than "Let's go! Hurry up!" "Get on the bus! Have a good day!" or "Good night! Go to bed!" :rofl:

7. Nov 5, 2008