Force required to hold a pendulum at an angle

In summary: The process of using the law of conservation of energy to solve for the minimum horizontal force leads to a different solution of F = mg/√(3). The veracity of this solution is uncertain and it is possible that there may have been a mistake in the process. In summary, the minimum horizontal force required to hold a simple pendulum at an angle of 60 degrees with the vertical is F = mg/√(3), although the accuracy of this solution is uncertain.
  • #1
kabirtomer
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What is the minimum horizontal force "F" required to hold a simple pendulum (mass "m") with string of length "l" at an angle of 60 degrees with the vertical. [ given answer = mg/√(3) , veracity uncertain ]This at first seemed simple enough, standard mechanics apply, leading to :
F/mg = tan(θ) where "θ" is the angle of the string from the vertical

here:
F/mg = tan(60)
F = mg√(3)

My second attempt, using the Law of Conservation of Energy, lead to this :
Taking "mean" position of pendulum as the Origin and Assuming that bob is brought up -
Final ( KE + PE ) (of bob) = Initial ( KE + PE ) + Work done on bob
mgl(1-cos(60)) = 0 + Work done by Tension + Work done by F
mgl(1-cos(60)) = 0 + 0 + F (l sin(60))
mgl/2 = Fl √(3)/2
F = mg/√(3)
huh.
Why would they give different solutions?
I am assuming I did something wrong.
I apologize if it is hard to understand, I have trouble conveying it without a diagram.
 
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  • #2
kabirtomer said:
What is the minimum horizontal force "F" required to hold a simple pendulum (mass "m") with string of length "l" at an angle of 60 degrees with the vertical. [ given answer = mg/√(3) , veracity uncertain ]This at first seemed simple enough, standard mechanics apply, leading to :
F/mg = tan(θ) where "θ" is the angle of the string from the vertical

here:
F/mg = tan(60)
F = mg√(3)


That is the correct solution. It is not a process, no sense to apply conservation of energy.
 

1. What is the force required to hold a pendulum at an angle?

The force required to hold a pendulum at an angle is directly proportional to the mass of the pendulum and the angle at which it is being held. The higher the mass and angle, the more force is needed to keep the pendulum in place.

2. How do I calculate the force required to hold a pendulum at an angle?

The formula for calculating the force required to hold a pendulum at an angle is F = m * g * sin(theta), where F is the force, m is the mass of the pendulum, g is the acceleration due to gravity, and theta is the angle at which the pendulum is being held.

3. What factors affect the force required to hold a pendulum at an angle?

The force required to hold a pendulum at an angle is affected by the mass of the pendulum, the angle at which it is being held, and the acceleration due to gravity. Other factors such as air resistance and friction may also have a minor impact on the force needed.

4. Why does the force required to hold a pendulum at an angle change?

The force required to hold a pendulum at an angle changes because the angle at which the pendulum is being held affects the gravitational force acting on it. As the angle increases, the gravitational force component along the direction of the pendulum also increases, thus requiring more force to hold it in place.

5. How does the length of the pendulum affect the force required to hold it at an angle?

The length of the pendulum has no direct effect on the force required to hold it at an angle. However, a longer pendulum will have a longer swing arc, which will result in a larger angle and thus require more force to hold it at that angle.

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