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Help me with a simple physics question

L

Lizabath

Member
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
 
Assuming no air resistance, what forces are acting on the ball? If you know the force(s), you will know the direction.
 
There is only one force, and thus the acceleration is the same no matter what point the ball is at. The answer doesn't change whether it is at its highest point or not.
 
Originally posted by: AgentEL
Assuming no air resistance, what forces are acting on the ball? If you know the force(s), you will know the direction.
Click to expand...

exactly.

I got it now.

Only one vector of force is acting on the ball, not two.

Thus the answer have to be Down. Acceleration -9.8 m/s^2 from gravity.
 
Originally posted by: AgentEL
Assuming no air resistance, what forces are acting on the ball? If you know the force(s), you will know the direction of the acceleration.
Click to expand...
With the inclusion of the portion added above, follow this advice.
 
break it down into horizontal motion and vertical motion
at the top of its flight, its not moving up or down.
however, it is still moving horizontally. I guess technically you've already applied the force, but its velocity would be only horizontal.
or something like that... im tired right now
 
Originally posted by: Lizabath
Originally posted by: AgentEL
Assuming no air resistance, what forces are acting on the ball? If you know the force(s), you will know the direction.
Click to expand...

exactly.

I got it now.

Only one vector of force is acting on the ball, not two.

Thus the answer have to be Down. Acceleration -9.8 m/s^2 from gravity.
Click to expand...


Yeah, that sounds better
 
Originally posted by: notfred
B. It's always B, regardless of the point in it's flight path (unless it's still in the pitcher's hand).
Click to expand...

yep. the force of gravity is constant from the time it leaves the guy's hand. assuming no air resistance, there are no other forces acting on the ball.
 
Originally posted by: Lizabath
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
Click to expand...

c. but the 'no air resistance' makes the problem unrealistic. Ball leaves the pitcher's hand with an initial acceleration (in x, y, z direction). The z-component of acceleration decreases due to gravity; at the highest point, the ball's z-acceleration is zero. But since 'no air resistance' is assumed, the ball would maintain its initial x- and y- acceleration which is obscure. Nothing stops the ball until it hits the ground or a fan's head.
 
Originally posted by: JDub02
Originally posted by: notfred
B. It's always B, regardless of the point in it's flight path (unless it's still in the pitcher's hand).
Click to expand...

yep. the force of gravity is constant from the time it leaves the guy's hand. assuming no air resistance, there are no other forces acting on the ball.
Click to expand...

3rd ed
 
Originally posted by: Peetoeng
Originally posted by: Lizabath
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
Click to expand...

c. but the 'no air resistance' makes the problem unrealistic. Ball leaves the pitcher's hand with an initial acceleration (in x, y, z direction). The z-component of acceleration decreases due to gravity; at the highest point, the ball's z-acceleration is zero. But since 'no air resistance' is assumed, the ball would maintain its initial x- and y- acceleration which is obscure. Nothing stops the ball until it hits the ground or a fan's head.
Click to expand...

boo yah!
 
Originally posted by: Peetoeng
Originally posted by: Lizabath
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
Click to expand...

c. but the 'no air resistance' makes the problem unrealistic. Ball leaves the pitcher's hand with an initial acceleration (in x, y, z direction). The z-component of acceleration decreases due to gravity; at the highest point, the ball's z-acceleration is zero. But since 'no air resistance' is assumed, the ball would maintain its initial x- and y- acceleration which is obscure. Nothing stops the ball until it hits the ground or a fan's head.
Click to expand...

Lot's of physics failures in the thread today.

Clarification: I'm talking about you. Oh, and maziwanka now it seems.
 
from the instant the ball leaves the hand, there is NO FORCE OTHER THAN GRAVITY acting on the ball. The horizontal speed (nor direction) is not changing (ie no acceleration) (there is no force in that dimension). The answer is B, and it is for the entire duration of the flight (not just the apex). The answer has been posted already I know, but there are also some wrong answers so I thought I would reiterate.

edit to clarify a little more -
the downward acceleration causes the balls vertical velocity to slow down on its way up, and increase on the way down. in both instances the direction of the acceleration is downward. also the ball is assumed to be travelling at a constant velocity after being launched from the hand.
 
Originally posted by: MacBaine
Originally posted by: Peetoeng
Originally posted by: Lizabath
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
Click to expand...

c. but the 'no air resistance' makes the problem unrealistic. Ball leaves the pitcher's hand with an initial acceleration (in x, y, z direction). The z-component of acceleration decreases due to gravity; at the highest point, the ball's z-acceleration is zero. But since 'no air resistance' is assumed, the ball would maintain its initial x- and y- acceleration which is obscure. Nothing stops the ball until it hits the ground or a fan's head.
Click to expand...

Lot's of physics failures in the thread today.

Clarification: I'm talking about you. Oh, and maziwanka now it seems.
Click to expand...
Beat me to it.
 
Originally posted by: MacBaine
Originally posted by: Peetoeng
Originally posted by: Lizabath
A baseball player throws a ball from left field toward home plate. Assume no air resistance, at the instant the ball reaches the highest point, what is the direction of the ball's acceleration? Why?

possible answers:
a. Up
b. Down
c. Horizontal
Click to expand...

c. but the 'no air resistance' makes the problem unrealistic. Ball leaves the pitcher's hand with an initial acceleration (in x, y, z direction). The z-component of acceleration decreases due to gravity; at the highest point, the ball's z-acceleration is zero. But since 'no air resistance' is assumed, the ball would maintain its initial x- and y- acceleration which is obscure. Nothing stops the ball until it hits the ground or a fan's head.
Click to expand...

Lot's of physics failures in the thread today.

Clarification: I'm talking about you. Oh, and maziwanka now it seems.
Click to expand...

i was wrong. its clearly b.

 
Tanswer is definitely not C. I'm glad to see i'm not the only one who got an A in physics in the thread.

Based on canonical assumptions, the answer is B (down). But the question gives a poor image in describing the reference frame. In the proper frame of reference, any of the answers could be true. The question really needs to establish a clear frame of direction before it can be answered fully.
 
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