Physics Help Forum Calculating the force...

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 Aug 3rd 2008, 03:27 PM #1 Junior Member   Join Date: Aug 2008 Posts: 1 Calculating the force... Hi, I am not sure if this is a math or a physics question. In a tennis game I have the following values for hitting a ball: I have the value of two points, a starting point and an ending point for a curve (the person who hits the ball, and where the ball lands) I also have gravity affecting the ball. And I have an additional value for a point the curve should be higher than (the net). If i want to calculate the vector for the force required on the ball in order for it to land on the ending point when hit from the starting point what is required of me? Thankyou
Aug 5th 2008, 06:08 PM   #2

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 Originally Posted by natasha Hi, I am not sure if this is a math or a physics question. In a tennis game I have the following values for hitting a ball: I have the value of two points, a starting point and an ending point for a curve (the person who hits the ball, and where the ball lands) I also have gravity affecting the ball. And I have an additional value for a point the curve should be higher than (the net). If i want to calculate the vector for the force required on the ball in order for it to land on the ending point when hit from the starting point what is required of me? Thankyou
You will need the velocity vector of the ball just after it leaves the racket. What you need to have to get that is the velocity vector just before the ball hits the racket and then have some way of measuring how the force is applied to the ball as the racket makes its swing. Effectively you are looking to use the Impulse-Momentum theorem to get the average force applied to produce the needed velocity for the ball to leave the racket.

As far as getting that velocity, it depends on what model for the motion you are using. If you are using the more realistic model using air resistance then you will have to settle for an approximate answer. If you are using the Galilean model (no air resistance, giving the usual motion equations) then you can get an exact answer. Either way all you will need is the final position and the other point you want the ball to pass through. Then you will end up with a system of equations (four equations in four unknowns) that you can either solve for exactly, or approximately.

If you need/want more help in setting this up, just let me know.

-Dan
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