Circular motion: find velocity with angle, mass, and radius

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SUMMARY

The discussion revolves around calculating the velocity required for a 200-gram ball to swing in a horizontal circle with a radius of 0.6 meters while maintaining a 34-degree angle with the horizontal. The correct velocity is determined to be 2.95 m/s. The user attempted various equations, including the tangent function and centripetal force equations, but struggled to arrive at the correct solution. Key concepts include the relationship between forces acting on the ball and the geometry of circular motion.

PREREQUISITES
  • Understanding of circular motion dynamics
  • Familiarity with trigonometric functions, specifically tangent
  • Knowledge of Newton's laws of motion
  • Basic principles of centripetal acceleration
NEXT STEPS
  • Study the derivation of centripetal force equations in circular motion
  • Learn how to construct and analyze Free Body Diagrams (FBDs)
  • Explore the relationship between angular velocity and linear velocity
  • Investigate the effects of mass on circular motion dynamics
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and circular motion, as well as educators seeking to clarify concepts related to forces and motion in a circular path.

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This was a homework problem; after five tries, I still did not get it, and I can't figure out how to get at the answer the assignment gave me. I could not find the answer anywhere that didn't get into angular velocity, which we are not at yet (and also did not give me the answer!).

1. Problem

How fast do you need to swing a 200-g ball at the end of a string in a horizontal circle of 0.6-m radius so that the string makes a 34∘ angle relative to the horizontal?

So we have:
mass: 0.2-kg (200-g)
radius: 0.6-m
angle: 34∘

Homework Equations


I have tried:
tan(34) = vy/vx, but that just got me dv, which was no help without time or period

tan(34) = v^2/r*g; this was wrong (and also did not take mass into account)

s = (v^2*sin(2*34))/g; I used the radius for s, which was a long shot, although this answer got me the closest (2.52 m/s)

m*(v^2/r) = +m*g + (-F), using grav in F=ma. obviously the acceleration was no gravity of Earth.

The Attempt at a Solution


The answer is apparently v=2.95 m/s

I have absolutely no idea how they got to this answer! I used any relevant-looking solution in the chapter this problem is from, I searched the web (including these forums), and no one else's problem had the solution. What was I doing wrong?
 
Physics news on Phys.org
If the ball travels in a horizontal circle, what is the net vertical force on the ball? What is the net horizontal force? What forces are acting on the ball? (What would a FBD look like?)
 

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