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# Isaac Physics Question Help: Ball Suspended by a Thread watch

1. Q: A small ball of mass m is suspended by a light thread. When a strong wind blows horizontally, exerting a constant force F on the ball, the thread makes an angle θ to the vertical. Using the terms provided, write an equation linking m, F, g and θ.

I have not been able to work this out, I got the equation (mg/cos(θ)) = squareroot(F^2 + (mg)^2) and do not know where I went wrong.
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3. (Original post by Exoid)
Q: A small ball of mass m is suspended by a light thread. When a strong wind blows horizontally, exerting a constant force F on the ball, the thread makes an angle θ to the vertical. Using the terms provided, write an equation linking m, F, g and θ.

I have not been able to work this out, I got the equation (mg/cos(θ)) = squareroot(F^2 (mg)^2) and do not know where I went wrong.
Have u drawn out a disgram of the situation.

U should find that u should be able to resolve the forces to find equations which show the forces acting on the ball acting in vertical and horizontal planes.
4. (Original post by Shaanv)
Have u drawn out a disgram of the situation.

U should find that u should be able to resolve the forces to find equations which show the forces acting on the ball acting in vertical and horizontal planes.
A diagram is given as a hint and I got (mg/cos(θ)) = squareroot(F^2 + (mg)^2), which is wrong, but I do not know where I went wrong so I am stuck.
5. (Original post by Exoid)
A diagram is given as a hint and I got (mg/cos(θ)) = squareroot(F^2 + (mg)^2), which is wrong, but I do not know where I went wrong so I am stuck.
I think u have tried to use pythagoras theorem to simplify the weight and horizontal force.

Although i appreciate what u are trying to do and cant give u a satisfactory explanation as to why it doesnt work i can guide u on the correct way to approach problems like this in the future.

Firstly resolve vertically then horizontally to obtain to equation.

Notice that the question doesnt mention the tension in the final equation. So u have to eliminate the tension force.

Do u have any ideas of how to move forward from here? If not let me know and ill help u a bit more
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7. (Original post by Stevenson Brown)
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Thank you for ur contribution it was really helpful and insightful.
8. (Original post by Shaanv)
I think u have tried to use pythagoras theorem to simplify the weight and horizontal force.

Although i appreciate what u are trying to do and cant give u a satisfactory explanation as to why it doesnt work i can guide u on the correct way to approach problems like this in the future.

Firstly resolve vertically then horizontally to obtain to equation.

Notice that the question doesnt mention the tension in the final equation. So u have to eliminate the tension force.

Do u have any ideas of how to move forward from here? If not let me know and ill help u a bit more
Ok, so next I tried resolving vertically then horizontally to obtain the equation, I used F as the horizontal and mg as the vertical and used trig to get θ the angle between the string and the vertical. So I did tan^-1(F/mg) to get θ. This is still incorrect and I am stuck again.
9. (Original post by Exoid)
Ok, so next I tried resolving vertically then horizontally to obtain the equation, I used F as the horizontal and mg as the vertical and used trig to get θ the angle between the string and the vertical. So I did tan^-1(F/mg) to get θ. This is still incorrect and I am stuck again.
Ok so heres how i would approach the question.

Firstly resolve vertically, this should give u an equation relating tension and mg.
Then resolve horizontally to get an equation in terms of F and tension.
Then u should be able to divide the two equations and get an equation independent of the tensions that relates all the variables mentioned in the question
10. (Original post by Exoid)
Ok, so next I tried resolving vertically then horizontally to obtain the equation, I used F as the horizontal and mg as the vertical and used trig to get θ the angle between the string and the vertical. So I did tan^-1(F/mg) to get θ. This is still incorrect and I am stuck again.
Try writing F = mg tan(θ)

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