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jonboy
07-06-2006, 07:55 PM
Can someone please very explicitily explain this problem to me:

Identify the graph that displays the speed of a baseball being pitched and then hit by a batter.

http://img368.imageshack.us/img368/2134/baseball6lm.png

I know the answer is not C and that D looks inaccurate.

tkhunny
07-06-2006, 08:05 PM
I don't like any of them.

I think it should slow down after the pitcher lets go. You have nothing like that.

Second, it should be very rapidly accelerated in the reverse direction, so it must go dramatically down to zero and speed up quickly.

It looks like "A" is the closest, but I really don't understand the notch on the end. I guess maybe that means it begins to slow down after the bat stops accelerating it?

Tough call.

pka
07-06-2006, 08:05 PM
Clearly,the answer is A.
When the ball is hit by the bat, its speed is zero. Right?

stapel
07-06-2006, 08:09 PM
Since the ball isn't moving under its own power, its speed must necessarily decrease after it has been accelerated (either by the pitcher or the batter).

Any increase in speed would be almost instantaneous, when one considers the time taken to pitch or hit a ball, compared with the time the ball is in the air, either between the mound and the plate or else between the plate and the ball's terminus.

If we could these very short acceleration periods, then we must start the ball at zero, have a short and sharp increase in speed, followed by a longer slight decrease. This is the pitch. Then the speed drops to zero (when the bat stops it), followed by another short and sharp increase, followed by a long slight decrease. Then the ball stops (by hitting the ground or being caught).

Assuming we consider the acceleration periods, only (B) come close. But since the pitch is in the air longer than in the pitcher's hand, (B) is not accurate.

If we include the drop to zero speed, then (A) would be best. But (A) shows the ball speeding up after it leaves the pitcher's hand, which is impossible. So (A) can't work.

And the lack of acceleration (this is a ball, not a rocket) eliminates (C) and (D).

I would not accept any of these plots as reasonable.

Eliz.

jonboy
07-06-2006, 08:10 PM
I don't like any of them.

Me either (but these were not ones I made myself). I guess my teacher needs more teaching or something.

When the ball is hit by the bat, its speed is zero. Right?

Yeah that is true. Thx all three of you for you assistance.

mcrae
07-06-2006, 09:21 PM
am i the only one who thinks that at time=0 (when it is in the pitcher's hands) the speed should also=0?

it couldnt be a imo.

Mrspi
07-06-2006, 11:07 PM
am i the only one who thinks that at time=0 (when it is in the pitcher's hands) the speed should also=0?

it couldnt be a imo.

You're not alone, mcrae....

Thus, I believe that B is the best (if not really good, but the best of the choices) representation for this situation.