What is the speed of the pitch?

  • Thread starter SirajK
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  • #1
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Homework Statement


A baseball player friend of yours wants to determine his pitching speed. You have him stand on a ledge and throw horizontally from an elevation 4.0 m above the ground. The ball lands 25 m away. What is his pitching speed?


Homework Equations


Kinematics Equations:
http://www.google.ca/imgres?imgurl=...AAzT5KPLeL30gHW3JDFBw&ved=0CD8Q9QEwAg&dur=255
 

Answers and Replies

  • #4
Spinnor
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Are you sure R should be 25 here?

I'm never sure, 8^)

What do you think it should be?
 
  • #5
HallsofIvy
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Your "kinematic equations" refer to the vertical motion only. You say the ball is thrown horizontally so the initial vertical component is 0. The height of the ball, at time t, is [itex]y= (1/2)(9.81)t^2+ 4[/itex]. Set that equal to 0 (the ball hits the ground) and solve for t to find when the ball hits the ground.

Taking "v" as the horizontal component of velocity, the distance the ball traveled, in time t, is given by x= vt. Put x= 25, t equal to the time you solved for above, and solve for v.

That, of course, is ignoring air resistance- which is fairly large for a baseball.
 
  • #6
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I'm never sure, 8^)

What do you think it should be?

Maybe it's the way the question is worded, but the figure of 25 to me seems to be the hypotenuse, rather than the adjacent for the triangle?


Your "kinematic equations" refer to the vertical motion only. You say the ball is thrown horizontally so the initial vertical component is 0. The height of the ball, at time t, is [itex]y= (1/2)(9.81)t^2+ 4[/itex]. Set that equal to 0 (the ball hits the ground) and solve for t to find when the ball hits the ground.

Taking "v" as the horizontal component of velocity, the distance the ball traveled, in time t, is given by x= vt. Put x= 25, t equal to the time you solved for above, and solve for v.

That, of course, is ignoring air resistance- which is fairly large for a baseball.

Check your signs here :)
 
  • #7
Spinnor
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You wrote,

"Maybe it's the way the question is worded, but the figure of 25 to me seems to be the hypotenuse, rather than the adjacent for the triangle?"

On second reading I agree, thanks for the correction.
 

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