you are swinging a .25 kg ball on a string above your head in a horizontal circle (at an angle) the length of the string is 1.5 m. It takes 1.2 s for the ball to make one revolution. Determine the angle the string makes relative to the horizontal.
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physics help please!!!
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gauchogolfer
macrumors 603
richard.mac
macrumors 603
you need to find out the radius which im not sure how to do and then use Sin^-1 to find the angle.
gusious
macrumors 65816
gauchogolfer
macrumors 603
Well, if I'm going to do his homework, I thought I'd at least make him think for a moment.
In order to solve this problem you need to make all of the forces on the weight balance out. The only two forces acting on the weight are gravity and the tension in the string. You know the direction that gravity is acting, and the force of the string is along the string itself.
By knowing the period of revolution, and the length of the string, you can determine the angular acceleration. Since the angular acceleration is proportional to the force acting inwards due to the string, you'll be able to sort out the angle necessary to apply such a force.
Looking at it again, it looks like there's no way to keep the weight above your head, since the string can't hold it up. What's to keep gravity from pulling it down?
Strange question actually.
chrmjenkins
macrumors 603
Yes you can if the question says it.
If you dont neglect gravity on this question, its not a question - there's nothing to keep the weight up! Unless there is data that the opening poster hasn't told us.
Totally depends what level the OP is doing physics at.
atszyman
macrumors 68020
The way I understand it is that the angle of the string is caused by gravity and therefore it cannot be neglected.
You have the ball at the end of the 1.5 m string with a certain angular acceleration which causes an outward force, adding to it the acceleration caused by gravity the 1.5 m string is the hypotenuse of a right triangle with sides set proportional to the outward force from the angular acceleration and gravity.
Flip richthomas's picture and r would be proportional to the angular force out, and the vertical side would be proportional to the gravitational acceleration, and then it's a trigonometry problem.
You have the ball at the end of the 1.5 m string with a certain angular acceleration which causes an outward force, adding to it the acceleration caused by gravity the 1.5 m string is the hypotenuse of a right triangle with sides set proportional to the outward force from the angular acceleration and gravity.
Flip richthomas's picture and r would be proportional to the angular force out, and the vertical side would be proportional to the gravitational acceleration, and then it's a trigonometry problem.