Thread: Stupid friday question

Here it is:

Lets say you are standing in the bed of a pickup truck traveling at 60 mph. You have the ability to throw a baseball at exactly 60 mph with no trajectory in the exact opposite direction of travel. The truck is traveling in a vacuum where gravity and wind speed are not a factor. What would happen to the ball, would it stop?

EDIT: with a trajectory parrellel to the direction of travel.

How can anything "go" with no trajectory? A trajectory can be parallel to the tangent plane of the earth's surface.

I would think so.

V = Vt + Vb = 60 + (-60) = 0

60 mph ??? my question is why do you throw like a 12 year old girl !

i think the baseball would stop and have no velocity from the point of where you released it.

Originally posted by Buster Highmen
How can anything "go" with no trajectory? A trajectory can be parallel to the tangent plane of the earth's surface.

No PROjectory? As in no catalyst I assume.

You'd fall out of the truck and hit your head (this is where that "acted upon by outside forces" comes in). These are trained professionals, don't try this at home.

I dunno. You should try it. HEY WATCH OUT FOR THAT SPEED BUMP!!!

Ahhhh...I just love these physics problems.

"Assuming you're in a vaccum, there's no gravity, no wind, no light, not even a spec of dust, or even the remotest sign of life and you're driving in a pickup at 30 mph and hawk a luggie out the back split window at 30 mph in the opposite direction. Will it hit the truck behind you right in the windshield and more importantly will the trucker get out at the next stop and kick your nerdy ass?"

1.2 Vehicle Motion at Constant Velocity
http://www-math.mit.edu/~djk/18_01/c...section02.html

A car moves so that at time t1 = 3s, its position p(t1) satisfies p(t1) = 6 yards from origin. At time t2 = 8s, p(t2) = 16 yards from origin.

Average velocity between t1 and t2 =p(t2)-p(t1) divided by t2-t1 which equals 10 yards divided by 5s = 2 yards / s

The velocity at time t1 is the average velocity between time t1 and t, with t very close to t1. How close? So close that the result doesn't depend on t.

[edit: Any questions?]

it would fall straight to the ground the truck was passing over. From the perspective of you in the truck it would apear to be traveling backwards at 60.

Originally posted by trainnvain
PROjectory?

It's only a projectory if it gets it for free.

Originally posted by Arty50
"Assuming you're in a vaccum, there's no gravity"

A world with no gravity, I shudder at the thought of this!

An interesting consideration:

Has anyone ever been in a boat on a day when the wind is blowing steadily at 10-15 kts, moving in the exact same direction and speed as the wind. When you stop, there is some decent chop in the water and you feel a very solid breeze, but at the same speed and direction you feel nothing. It feels as if you are caught in a vacuum (second hand information). It is amazingly calm when everything around you is turbulent. Pretty cool.

In an unrelated sidenote: Beaver, please replace current avatar with the naked-boobie version of a few days ago. Thank you.

Originally posted by Telephil
The truck is traveling in a vacuum where gravity and wind speed are not a factor.

Gravity is still a factor.

without quoting equations. You answer is:

The ball would travel at 60mph away from you at a total velocity of 120mph, because it is already starting with the velocity that it has from riding in the back of the truck. Since it is a vacumn, there is no wind resistance, but you would need gravity, which eventually would have it fall to the ground.


right??

As viewed from a person standing on the side of the road, the baseball would come to a sudden stop (remember that prior to being released the baseball is travelling at 60 mph) and fall to the ground.

A far more interesting demonstration of relativistic motion can be seen at one of the Paris science mueseums (and likely other science museums). They have a large circular room, that spins fairly slowly (10 - 20 rpm?). Inside this room is a bunch of foam balls, and targets painted on the walls. When you throw the balls, they end up curving and hitting the wall about 5 feet away from wherever you aimed. Even though you know what's going on, it's still extremely disorienting and funny.

Originally posted by Viva
Gravity is still a factor.

I guess if gravity is not a factor an observer standing on the ground would see the ball leave the thrower's hand and remain motionless at the exact height it was thrown for perpetuity.

But please kids, don't try this at home

Originally posted by Crinkle
but you would need gravity, which eventually would have it fall to the ground.


right??

No, you don't need to consider gravity. It there's no gravity the ball is in static equilibrium and will remain motionless from the perspective of a person standing on the ground (ok, someone NAILED to the ground since there's no gravity!).

Originally posted by Telephil
Here it is:

The truck is traveling in a vacuum where gravity and wind speed are not a factor. What would happen to the ball, would it stop?

yes.

´COS YOU ALL BE DEAD,´ COS YOU COULDNT BREEATHE!!!

Originally posted by The AD
No, you don't need to consider gravity. It there's no gravity the ball is in static equilibrium and will remain motionless from the perspective of a person standing on the ground (ok, someone NAILED to the ground since there's no gravity!).

There cannot be any ground, or person, if there's no gravity.

The ball would have zero velocity relative to the ground and be motionless (trajectory-free).

edit: I should read before posting.

Originally posted by Crinkle
without quoting equations. You answer is:

The ball would travel at 60mph away from you at a total velocity of 120mph, because it is already starting with the velocity that it has from riding in the back of the truck. Since it is a vacumn, there is no wind resistance, but you would need gravity, which eventually would have it fall to the ground.


right??

Umm, no. think about it in terms of Vectors (remember HS Physics?)

60<- plus 60-> would equal O horizontal movement. If there's gravity the ball would drop straight down from the point of release, accelerating at 9.8m/sec squared per G. Since the original truckbed baseball throw occurred in space (vacuum, no gravity) the ball would hang motionless at said point of release until acted upon by an outside force (inertia.)

NEXT!!

Originally posted by Tippster
Umm, no. think about it in terms of Vectors (remember HS Physics?)

60<- plus 60-> would equal O horizontal movement. If there's gravity the ball would drop straight down from the point of release, accelerating at 9.8m/sec squared per G. Since the original truckbed baseball throw occurred in space (vacuum, no gravity) the ball would hang motionless at said point of release until acted upon by an outside force (inertia.)

NEXT!!

your right tippster, I misread "in the exact opposite direction" I agree with you, appear to drop straight to the ground. I was doing physics while on conference call.

[entering nerd mode]. It would almost stop. Throwing the ball would cause a small force on the truck, speeding it up to 60.01mph an hour or something like that during the throw. So upon release the thing would be going about .01 mph in the direction of the truck. [/exiting nerd mode]

damnit i'm a loser.

Originally posted by cmor
[entering nerd mode]. It would almost stop. Throwing the ball would cause a small force on the truck, speeding it up to 60.01mph an hour or something like that during the throw. So upon release the thing would be going about .01 mph in the direction of the truck. [/exiting nerd mode]

damnit i'm a loser.

You're right. Nice catch you loser!

I'm still not sure how that truck stays on the road with no gravity, though.

Originally posted by The AD
You're right. Nice catch you loser!

I'm still not sure how that truck stays on the road with no gravity, though.

If there's a truck, there's gravity. If there's a road...