Wind drag problem with a ball hanging on a rope

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SUMMARY

The discussion centers on solving the wind drag problem involving a 1.2 kg ball suspended from a rope at a 25-degree angle due to a horizontal wind speed of 15.0 m/s. The correct approach involves recognizing that the drag force exerted by the wind is equivalent to the x-component of the tension in the rope. The final calculated drag force is 5.84 N, derived from the relationship between the tension and the angle of the rope. Participants emphasized the importance of accurately drawing the free body diagram (FBD) to visualize the forces acting on the ball.

PREREQUISITES
  • Understanding of free body diagrams (FBD)
  • Knowledge of trigonometric functions (sine, cosine, tangent)
  • Familiarity with Newton's second law of motion (Fx = ma)
  • Basic principles of forces acting on objects in equilibrium
NEXT STEPS
  • Study the principles of tension in ropes and angles in physics problems
  • Learn how to accurately draw and interpret free body diagrams
  • Explore the relationship between drag force and wind speed in fluid dynamics
  • Investigate the effects of different angles on tension and drag in similar scenarios
USEFUL FOR

Physics students, educators, and anyone interested in understanding forces acting on suspended objects in windy conditions.

crememars
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Homework Statement
A 1.2 kg ball is hanging from the end of a rope. The rope hangs at an angle of 25 degrees from the vertical when a 15.0m/s horizontal wind is blowing. If the wind’s force on the rope is negligible, what drag force does the wind exert on the ball?
Relevant Equations
the answer is 5.84 N
1665924593232.png

I drew a FBD but I feel like it's wrong because there are too many missing values. I tried this:

Fy = 0
Tcosθ - Fg = 0
Tcosθ = mg
T = (1.2)(9.8) / cos(25)
T = 12.98 N

Fx = ma
Fwind - Tsinθ - Fdrag = ma
Fwind - (12.98)(sin25) - Fdrag = ma

I don't know how to find these missing values. I feel like I'm approaching the situation wrong? I saw one solution solve it like this:

g(tanθ) = a
(9.8)(tan25) = 4.57

Fx = ma
Fx = (1.2)(4.57)
Fx = 5.48 N

but this doesn't make any sense to me.

any help would be appreciated, thank you !
 
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crememars said:
Homework Statement:: A 1.2 kg ball is hanging from the end of a rope. The rope hangs at an angle of 25 degrees from the vertical when a 15.0m/s horizontal wind is blowing. If the wind’s force on the rope is negligible, what drag force does the wind exert on the ball?
Relevant Equations:: the answer is 5.84 N

View attachment 315675
I drew a FBD but I feel like it's wrong because there are too many missing values. I tried this:

Fy = 0
Tcosθ - Fg = 0
Tcosθ = mg
T = (1.2)(9.8) / cos(25)
T = 12.98 N

Fx = ma
Fwind - Tsinθ - Fdrag = ma
Fwind - (12.98)(sin25) - Fdrag = ma

I don't know how to find these missing values. I feel like I'm approaching the situation wrong? I saw one solution solve it like this:

g(tanθ) = a
(9.8)(tan25) = 4.57

Fx = ma
Fx = (1.2)(4.57)
Fx = 5.48 N

but this doesn't make any sense to me.

any help would be appreciated, thank you !
You have too many forces on your diagram. The force from the wind is the force of the drag. So you only have the force from the wind acting to the right.

-Dan
 
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topsquark said:
You have too many forces on your diagram. The force from the wind is the force of the drag. So you only have the force from the wind acting to the right.

-Dan
I think I understood, thank you! so the drag would be equal to the x component of the tension.
 
crememars said:
I think I understood, thank you! so the drag would be equal to the x component of the tension.
Yes.

-Dan
 
topsquark said:
You have too many forces on your diagram. The force from the wind is the force of the drag. So you only have the force from the wind acting to the right.

-Dan
Would that not make it 4.97 N if it is equal to the x-component of the tension in the string?
 
No.
But if you show how you get this value, someone may figure out the error.
 
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It helps to draw your diagram approximately to scale. Then you can tell if the answer you came up with is in the ballpark (sanity check). If you draw the correct arrangement of the 1.3kg force vector on the ball, the drag vector you are solving for, and the 25-degree angle in the right place, that will be everything you need.
 
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