Projectile Question

[rarisgod]

Hey guys, it's me again. I have a question which this time involves projectile motion (i believe) however it's been 2 years since my physics class, so I don't remember how to do it lol. Here goes;

A ball leaves a throwers hand 1.58 m above the ground. It has an initial vertical velocity of 8.9 m/s and an initial horizontal velocity of 18.53 m/s.
1. How high will it go above the point of release?
2. What is it's maximum height above the ground?
3. How long will the ball be in the air until it returns to the original release height?
4. How far will the ball go in the horizontal direction before it returns to it's original release height?*

I notice that (exceptfor number 2) it usually mentions the original release height, which to me seems like it will be a bit easier than calculating if it went back to the ground.

[eastcoasteddie]

THE ABSOLUTE BEST way to remember math/physics and everything else. Scroll down the page and see the projectile motion videos!

http://www.khanacademy.org/

I ALWAYS practice with this.

[DerHoggz]

1:
(v_{finalvertical})²=(v_{initialvertical})²+2ax

v_{finalvertical} would equal zero since you are looking for the highest point, which will be the instant when the ball has no velocity and is about to begin falling down.

a would be the acceleration due to gravity (-9.81 m/s²)

2:
The answer to 1, plus height of point of release

3:
2((v_{finalvertical}-v_{initialvertical})/a)

4:
v_horizontal((answer to number 3))

[champbassist]

This page has all the formulae and explanations on projectiles you could need:

http://library.thinkquest.org/10139/small/proj1.html

[thefruitfarmer]

The speed of sound is 330ms per foot.

[champbassist]

Originally Posted by thefruitfarmer

The speed of sound is 330ms per foot.

NO. Speed of sound = 330 metres/second. It's 1082.4 ft/s. ms/ft is not a unit of speed.

Thanks for the post, though. Notwithstanding the utter lack of relevance or accuracy.

[thefruitfarmer]

Originally Posted by champbassist

NO. Speed of sound = 330 metres/second. It's 1082.4 ft/s. ms/ft is not a unit of speed.

Thanks for the post, though. Notwithstanding the utter lack of relevance or accuracy.

You're welcome - hope that helps!

The other one I remember is it takes roughly a quarter of a second for sound to travel 100 yards - the length of a football pitch.

[bassybill]

This spreadsheet could be edited a bit to sort out your question.

You're welcome.

[champbassist]

Originally Posted by thefruitfarmer

You're welcome - hope that helps!

Erm... how's it supposed to help if it's not correct?

[MakiSupaStar]

Do your own homework.

[thefruitfarmer]

Originally Posted by champbassist

Erm... how's it supposed to help if it's not correct?

What I meant to say was sound travels 330 metres per second or roughly 1 millisecond per foot.

This is useful for a bass player to know, as in practice every foot you move away from your speakers will result in 1 millisecond (approx) "latency" between you hitting the strings and hearing the note. Consequently, you will need to compensate for this time lag in your playing to get a good groove.

Without this knowledge you will need to understand projectile motion. If you can calculate the path of missiles thrown at you by disgruntled members of the audience then you can establish how far you have to step to the side to avoid rotton fruit, beer bottles etc.

[Chebass88]

I need to start posting my homework problems on TB. Forget this staying up until 2Am trying to figure it out myself!

[lunarpollen]

Wouln't the exact figure also depend on air temperature/density, wind velocity/direction, the size and mass/density of the ball, the surface texture of the ball, spin imparted on the ball by the thrower, etc.?

[Chebass88]

Originally Posted by lunarpollen

Wouln't the exact figure also depend on air temperature/density, wind velocity/direction, the size and mass/density of the ball, the surface texture of the ball, spin imparted on the ball by the thrower, etc.?

Absolutely, however, this is a first year of college / HS physics problem. All of those things are ignored for a first approach. The answers are off by a little bit, but for the purposes of teaching vectors and very basic calculus, it isn't all that bad. All of the things you mentioned require some higher order maths or physics / engineering courses, which the OP has not likely had at this point.

In this case, the frictionless / resistance-less case would be the furthest, with all other variants coming up short.

Then again - what is the level of detail the answer requires?

ian

[champbassist]

Originally Posted by MakiSupaStar

Do your own homework.

Good point.

[Philonius]

"Without this knowledge you will need to understand projectile motion. If you can calculate the path of missiles thrown at you by disgruntled members of the audience then you can establish how far you have to step to the side to avoid rotton fruit, beer bottles etc."

Shoes.

[rarisgod]

Originally Posted by Chebass88

I need to start posting my homework problems on TB. Forget this staying up until 2Am trying to figure it out myself!

I understand completely the value of figuring it out myself. I've done projectile motion before, but I couldn't remember how to do it as I don't take Physics anymore. I was mainly just looking for a way to understand it myself so I could explain it and help them to understand and be able to figure out future problems.

These answers aren't for me, they're so that I can refresh my memory so I'm able to help someone else figure it out.

Thanks for all those who were helpful, I'll let you know how this goes when I get a chance to work with her again (might not be until Friday).

[champbassist]

Originally Posted by rarisgod

Thanks for all those who were helpful, I'll let you know how this goes when I get a chance to work with her again (might not be until Friday).

So we're helping you understand stuff and you're taking all the credit by helping 'her'?

[DerHoggz]

The three most important things for physics are:

1. algebra
2. formulae
3. unit math

All IMO of course, also not so much for calculus based.

[UncleFluffy]

The problem is poorly defined. Where is the thrower?