Homework Help: physics

Posted by Anonymous on Saturday, November 28, 2009 at 7:00pm.

A tennis ball on a string is being swung in a horizontal circle of radius r. The ball has mass m and the string length l. Which expression gives the magnitude of the tension T in the string in terms only of the speed v of the ball and of m, r, and l?

Answer choices
1. T=mgr/l
2. T=0, as is always the case for a conical pendulum.
3. T=mv^2/l
4. T=mv^2/r
5. T=m[g−(v^2/r)]
6. T=mv^2/2
7. T=mg
8. T=m[g+(v^2/r)]
9. T=mv^2l/r^2

physics - MathMate, Saturday, November 28, 2009 at 10:11pm
I do not see where the length of the string (l) comes in the picture if the radius of the circular motion is fixed at r.

If the ball is swung in air where it is allowed to sag, then there is the horizontal component equal to mv²/r and the vertical component equal to mg.
The vectorial sum is
m*sqrt(g²+(v²/r)²)
which does not correspond to any of the options listed, unless the square-root sign (√) is missing from choices 5 and 8.
physics - SA, Wednesday, October 20, 2010 at 7:49pm
4
physics - YW, Saturday, March 2, 2013 at 10:26pm
Actual Answer is 9

SA's answer of 4 is false, I tried it out personally, it doesn't work

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