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

In summary, the problem is about finding the required speed for a 200-g ball on a 0.6-m radius horizontal circle with a 34∘ angle relative to the horizontal. After multiple attempts, the answer is apparently v=2.95 m/s, but the student is unsure how to get to this answer. They tried using various equations and searching online, but could not find a solution. The student also mentions considering the net vertical and horizontal forces on the ball and drawing a free body diagram.
  • #1
ecalop
1
0
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?
 
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  • #2
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?)
 

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

1. How do I calculate the velocity of an object in circular motion?

To find the velocity of an object in circular motion, you will need to know the angle, mass, and radius of the object. You can use the formula v = ωr, where v is the velocity, ω is the angular velocity (measured in radians per second), and r is the radius of the circular path.

2. What is the relationship between velocity and radius in circular motion?

The velocity of an object in circular motion is directly proportional to the radius of the circular path. This means that as the radius increases, the velocity also increases, and vice versa.

3. Can I use any units for velocity, angle, mass, and radius in the circular motion formula?

Yes, you can use any units for velocity, angle, mass, and radius as long as they are consistent. For example, if you use meters for the radius, you should also use meters for the velocity and kilograms for the mass.

4. What happens to the velocity if the angle changes in circular motion?

The velocity will change if the angle changes in circular motion. This is because the angular velocity (ω) is determined by the angle and is constant. Therefore, a change in angle will result in a change in velocity.

5. Can I use this formula for any type of circular motion?

This formula can be used for any type of circular motion, as long as the object is moving at a constant speed. If the speed changes, you will need to use a different formula that takes into account the acceleration of the object.

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