Yes, but I thought the truck continued on driving? The line was just when the ball was shot? And you would have to be REAL good to get it shot and brake at the exact same time.

Sal, the truck keeps going as far as the original statement is concerned

Yeah it is in the question posted by Paul, I was just saying that the ball would be on the line if their were both positive and negative accelerations at the same time in a situation like the truck stopping and the cannon firing.
The question is hypothetical so factors like wind resistance, friction, precision, and the drivers BAC don't matter.

Drivers BAC lol. But even then, wouldn't the ball still have negative velocity? Assuming the truck is positive velocity and yes I know, can't be negative but you get what I am saying. The ball would have zero relative velocity to an on looker but wouldn't it still accelerate?

Velocity can be negative it would mean that the ball is slowing down. You can relate positive and negative with direction of forces, (foreword = positive, backwards = negative) but that doesnt have much to do with the question. When a change in velocity occurs there is a change in acceleration.

I'm not sure exactly what you mean but I think it's this. In the original question the ball is traveling with the truck at 55mph and it positively accelerates to reach a velocity of 55mph traveling away from the line.

In the case where the truck stopped on the line and the ball is fired the ball has no velocity but is acceleration in opposition with the truck which is why it goes no where.

No.
Think of like a fly in your car. It flys around like it normally would, not at 55mph if the car is going 55mph. It flys at a relative speed to the car.
The ball already moving at 55mph relative to the ground, but zero mph relative to the truck. So it would be going 55mph off the back of the truck, and at the moment of the trigger firing the ball, the ball would go 55mph off the back end of the truck.

Not that hard to figure out.

it would shoot out at 55 mph in the opposite direction if fired at 90 degrees to the ground. if you shot it straight up, factoring out all resistance, it would land back in the truck. an object in motion tends to stay in motion except.....

Nope. The truck would have forward motion whereas the projectile only has vertical motion.

..when acted upon by another object.


Newton's First Law of motion.

object is shot backward, NOT up.

negative, i'll try to find the video. its like driving in a car and throwing a ball up in the air. it doesn't fly to the back of the car, it goes straight up and down even though the car is moving.

Yea I had a brain fail. I was thinking wind.

I am going to have to say no. I have my reasons.

Next question....

http://i140.photobucket.com/albums/r...nturntable.jpg


:)

No.

:rofl: wait roflcopter or whatever it is.

yeah if you factor wind it changes, but still the same principle. its like pegging water bottles or munchcins at street signs, you throw a little early and wait to here the bang.

no. it will land some 100 feet behind the line (as the truck moves ahead of the line).

i'm going to say yes just to be a D-bag......55mph reverse relative to the truck at 55mph is 0mph relative to the ground so ignoring the fact that the negative air pressure behind the truck is going to cause the ball to fallow the truck and ignoring the potential spin on the ball(unless fired from a riffled barrel) the ball will land on the line

You didnt need to say all that for us to think that.

o I know, but its so much more fun to...