Conical pendulum: what are the tension and the angle?

In summary, the conversation discusses finding the tension in a string holding a 1.5 kg rock whirled in a horizontal circle with a constant speed of 5 m/s. There is some debate over whether the given information is enough to solve the problem and the preferred method of solving. The relevant equations are mentioned, including Fc = mv^2/r and W = mg. The question is also raised about the relationship between sin and cos.
  • #1
pkc111
225
26
Homework Statement
A rock with a mass 1.5 kg is being whirled in a horizontal circle on a string 0.8 m long. The speed of the rock is a constant 5 m/s. Find the magnitude and direction of the tension in the string.
COMMENT: There seems to be too many unknowns here.
Relevant Equations
Fc = mv2/r
W = mg
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1585533348673.png
 
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  • #2
pkc111 said:
Homework Statement:: A rock with a mass 1.5 kg is being whirled in a horizontal circle on a string 0.8 m long. The speed of the rock is a constant 5 m/s. Find the magnitude and direction of the tension in the string.
COMMENT: There seems to be too many unknowns here.
Relevant Equations:: Fc = mv2/r
W = mg

View attachment 259616View attachment 259617
So what is cos2(θ) in terms of sin(θ)?

By the way, it is far better style to keep everything algebraic. Don't plug in numbers until the end. For one thing, more people will take the trouble to check your work.
 
  • #3
Thank you for your reply.
Are you saying that this question is solvable with the information provided in the question?
 
  • #4
Cos my gut feeling is the question is wrongly written ..as every other question in this high school physics textbook chapter needs only very straightforward maths...Is someone able to say whether the information is enough to define a specific conic pendulum case which is solvable?
 
  • #5
pkc111 said:
Thank you for your reply.
Are you saying that this question is solvable with the information provided in the question?
In your last equation in post #1 there is only one unknown, so it should be solvable.
I repeat, what equation relates sin to cos (and involves no other trig function)?
 

1. What is a conical pendulum?

A conical pendulum is a type of pendulum where the bob (weight) moves in a circular motion rather than a back-and-forth motion. It is suspended by a string or rod and swings in a conical shape rather than a straight line.

2. How is the tension in a conical pendulum calculated?

The tension in a conical pendulum is calculated using the equation T = mgcosθ, where T is the tension, m is the mass of the bob, g is the acceleration due to gravity, and θ is the angle between the string and the vertical. This equation is derived from the centripetal force acting on the bob.

3. What factors affect the tension in a conical pendulum?

The tension in a conical pendulum is affected by the mass of the bob, the length of the string, the speed of the bob, and the angle of the string with the vertical. Any changes in these factors will result in a change in tension.

4. How does the angle of the string affect the motion of a conical pendulum?

The angle of the string affects the motion of a conical pendulum by determining the tension in the string. As the angle increases, the tension decreases, resulting in a larger circular motion and slower speed of the bob. As the angle decreases, the tension increases, resulting in a smaller circular motion and faster speed of the bob.

5. Can the angle of a conical pendulum be greater than 90 degrees?

No, the angle of a conical pendulum cannot be greater than 90 degrees. This is because the tension in the string would become negative, which is not physically possible. The maximum angle for a conical pendulum is 90 degrees, where the tension in the string is equal to the weight of the bob.

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