another debate...... - NJFBOA - Home of New Jersey's Camaros and Firebirds

V · 10-22-2008, 01:12 PM

For all those that got so wound up over the plane thread.... this is for you guys...

and no kasey, no "f the plane"

ok, i first brought this up the other day to a few board members while working on another members car... and i loved the looks i got so i decided to bring it on here...

You are given a tennis ball launcher, capable of a consistant muzzle velocity of 55mph. The launcher is mounted facing rearward in the bed of a small truck. The truck now drives down the road and sets the cruise control at exactly 55mph. There is a line painted across the road further down, and as the rear bumper of the truck finally crosses that line, the tennis ball launcer is fired. Does the ball land on the line? For all intents and purposes, we will NOT factor in wind and/or air resistance.

...now GO... lol

Anti_Rice_Guy · 10-22-2008, 01:21 PM

It depends when the ball is launched and the delay of the launcher, but with those being perfect, I would think so.

WildBillyT · 10-22-2008, 01:23 PM

Angle of the barrel parallel to the ground I assume?

SteveR · 10-22-2008, 01:25 PM

damn dude, I'm going to be thinking about his all day now

If there's no wind resistance, then the test would be done in a vacuum, and that makes it all the more complicated

I'd say that even though the truck is moving at 55mph, and the launcher launches the ball at 55mph, muzzle velocity decreases over distance, so even though the truck is moving at the same rate as the ball in the exact opposite direction, the ball will slow down over its trajectory path, whereas the truck will not, so the ball will still land past the line. Even though the ball may not be moving in terms of its relation to the ground, its reference for distance is the object of which it was launched from, not landing on. I had to analyze something like this in terms of SAMs and Airborne Weapons Systems before, so I'm biased

And I'm assuming we are guessing where the ball will land and not take into consideration the ball rolling, and the levelness of the floor of which it lands

NJSPEEDER · 10-22-2008, 01:29 PM

To make the ball land on the line, you would have to time the firing of the gun with the barrel acceleration so as to put the ball above the line when it reaches 55mph.

The rear bumper of the truck is not really a part of the equation. Excess information that will distract a lot of people away from a correct answer.

The theory is sound, what isn't is a trigger system. Someone get MythBusters on this ASAP. lol

-Tim

cdacda13 · 10-22-2008, 01:33 PM

No, I think.
Reasons:
The launcher is traveling at 55 mph in the opposite direction as it firing, so it negate the launch of the tennis ball to a certain degree. To figure out how much, probably requires tons of math that I have no idea/desire to do.

WildBillyT · 10-22-2008, 01:38 PM

Quote:

Originally Posted by cdacda13

No, I think.
Reasons:
The launcher is traveling at 55 mph in the opposite direction as it firing, so it negate the launch of the tennis ball to a certain degree. To figure out how much, probably requires tons of math that I have no idea/desire to do.

More than math, it takes a knowledge of physics. Based on how much you "ignore" you can make it go either way.

GP99GT · 10-22-2008, 01:51 PM

Quote:

Does the ball land on the line?

Short answer: no.

Long answer: no, it wont.

If i had a degree in physics it could be explained

LTb1ow · 10-22-2008, 01:59 PM

The truck/cannon is moving at the same speed, so the cannon will only accelerate the ball further. So the ball will land pretty far back.... whys that hard?

SteveR · 10-22-2008, 02:05 PM

ok, I think I got it. Taking all wind resistance out of the equation, balls location at first contact with the floor is measured by muzzle velocity efficiency x altitude of center bore of barrel to the floor.

LTb1ow · 10-22-2008, 02:06 PM

Yea.... the only hard part is if you want the relative velocity wrt to the truck or a viewer on the ground.....

V · 10-22-2008, 02:07 PM

ill clear up some...

barrel is perfectly level and parrellel to the ground

& to clear up directions, Truck is travelling EAST, barrel is facing WEST.

launcher fires by an automatic trigger that senses the line., so that the ball leaves the barrel exactly as the muzzel passes over the line.

landing/bouncing on the line is still considered the same, rolling would only happen after initial contact anyway.

SteveR · 10-22-2008, 02:09 PM

Quote:

Originally Posted by Shownomercy

Yea.... the only hard part is if you want the relative velocity wrt to the truck or a viewer on the ground.....

measuring muzzle velocity efficiency based on the weapon systems measured capabilities, not perception.

SteveR · 10-22-2008, 02:10 PM

Quote:

Originally Posted by SmokingSS

ill clear up some...

barrel is perfectly level and parrellel to the ground

& to clear up directions, Truck is travelling EAST, barrel is facing WEST.

launcher fires by an automatic trigger that senses the line., so that the ball leaves the barrel exactly as the muzzel passes over the line.

landing/bouncing on the line is still considered the same, rolling would only happen after initial contact anyway.

you'd want to measure timing by having the trigger engage when the chamber passes over the line, not muzzle, as when the ball is leaving the muzzle, it's already moving.

LTb1ow · 10-22-2008, 02:12 PM

Still don't see the question here, are you looking to see if the ball will hit the line at a certain velocity or just hit the line? Cause if it fires when it crosses the line and it shoots at 55mph there is no way its gonna hit the line.

Kojak · 10-22-2008, 02:17 PM

Let’s assume there is instantaneous acceleration to 55mph when the ball is fired, there is a constant velocity of 55mph, no wind or air resistance, gravity is pulling down at 32ft/s squared, and the driver has a life and doesn’t care about this jack ass question lol.

Due to the balls constant velocity of 55mph and not acceleration the ball is inert.
Here is an example:
We are on Earth which is has an almost constant rotating speed, the Earth is in orbit at an almost constant speed, and the solar system within the galaxy is traveling at an almost constant speed. All of these constant forces do not affect us because they are happening all the time so technically we are inert to these constant forces as we go along our daily lives.

It’s kind of hard to imagine a world where objects are affected by constant velocity because it’s not possible in this universe, if you want to talk about other universes with different laws of physics its hard to understand because they don’t exist in our plane of existence.

Anyway so as the ball is traveling and it is unaffected by the constant velocity so it will shoot back horizontally at 55mph on the line where it is fired and land 101.682feet away (this doesn’t account for the height it was fired at).

x2 = vo2 + 2(a)*(x-xo)

x = ?
xo = 0
vo = 55mph = 80.67 ft/s
a = -32ft/s2

02 = (80.67ft/s)2 + 2(-32ft/s2) * (x – xo)
0 = 6507.64ft2/s2 - 64ft/s2 (x)
-6507.64ft2/s2 = -64xft/s2
101.68ft

This is high school stuff people...

LTb1ow · 10-22-2008, 02:18 PM

Your just the only one willing to write it all out.... lol

Kojak · 10-22-2008, 02:21 PM

Quote:

Originally Posted by Shownomercy

Your just the only one willing to write it all out.... lol

Its procrastination at its best, I have a mid term at 7 and I don’t care for it lol…

GP99GT · 10-22-2008, 02:28 PM

sal just blew my mind

enRo · 10-22-2008, 02:38 PM

Nope. The launcher has to be practically dragging on the ground in order for the ball to land on the line... cuz if you look at it this way.. Do the same exact thing Paul first explained, then imagine if you were driving on planks 20 feet in the air and the line is on the ground 20 feet below the truck. The ball is not gonna land on that line because it will still have a forward motion reguardless if its shot backwards at the same speed. Thats my take...

Also, F the Launcher.

LTb1ow · 10-22-2008, 02:42 PM

The height of the launcher has little or nothing to do with it. The ball is given more velocity than the truck so its not gonna hit the line whether or not the launcher is 1 foot above ground or 30. Imagine the truck stopped at the line and then the ball is shot, same thing.

Knipps · 10-22-2008, 02:53 PM

It's not hitting the line.

enRo · 10-22-2008, 03:16 PM

Quote:

Originally Posted by Shownomercy

The height of the launcher has little or nothing to do with it. The ball is given more velocity than the truck so its not gonna hit the line whether or not the launcher is 1 foot above ground or 30. Imagine the truck stopped at the line and then the ball is shot, same thing.

Technically no, because the truck is still in a forward motion. At work, when I spit off the back of a moving garbage truck in the opposite direction its moving in, it will catch up to me, not quite, but it still moves forward. But that also has wind factored in.

I will have to conduct this type of experiment at work, since im legally allowed to hang off a garbage truck going 40 mph... ill just have to toss a tennis ball backwards

LTb1ow · 10-22-2008, 03:22 PM

Without wind, the trucks motion will have nothing to do with the ball though....

If you throw a ball in a train, will the ball go nowhere? No, its all relative.

Kojak · 10-22-2008, 03:31 PM

Quote:

Originally Posted by Shownomercy

The height of the launcher has little or nothing to do with it. The ball is given more velocity than the truck so its not gonna hit the line whether or not the launcher is 1 foot above ground or 30. Imagine the truck stopped at the line and then the ball is shot, same thing.

The ball is moving at 55mph and it is not directly connected to the truck so when it suddenly stops the ball will want to move foreword with a force of 55mph.

So if the truck was moving at 55mph then stopped on the line that is a negative acceleration from 55mph to 0mph. The ball will be shot at a positive acceleration from 0mph to 55mph. If these two accelerations occur at the same moment then the ball will not travel anywhere.