Finding acceleration from the angle made by a hanged ball.

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Homework Help Overview

The discussion revolves around a physics problem involving a ball suspended in a bus, which makes an angle of 18° when the bus accelerates. Participants are exploring the relationship between the angle of the rope and the acceleration of the bus, focusing on the forces acting on the ball.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relevance of air resistance and the forces acting on the ball, including gravity and tension in the rope. There are suggestions to draw a free body diagram to better understand the situation. Questions are raised about the behavior of objects inside the bus and how they relate to the bus's acceleration.

Discussion Status

The discussion is active, with participants engaging in reasoning about the forces on the ball and the implications of the angle formed by the rope. Some guidance has been offered regarding the use of free body diagrams, and participants are considering the implications of their observations.

Contextual Notes

Participants are operating under the assumption that air resistance can be ignored due to the bus's motion. The problem context involves understanding the dynamics of a system in acceleration and the forces acting on a suspended object.

Mohamed BOUCHAKOUR
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Homework Statement


A ball with a mass of 200g, is hanged on the roof of a bus with a rope (it's mass is negligible), when the bus starts moving, the rope makes an angle of 18°.
What's the acceleration of the bus?

Homework Equations


ΣF=m.a

The Attempt at a Solution


The first thing i thought of is air friction, but it related to speed not acceleration, and the ball is inside the bus, it would be negligible.
Nothing exept that came to my mind.
 
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You're right, air resistance is not an issue because the air moves with the bus. How about drawing a free body diagram?
 
Mohamed BOUCHAKOUR said:

Homework Statement


A ball with a mass of 200g, is hanged on the roof of a bus with a rope (it's mass is negligible), when the bus starts moving, the rope makes an angle of 18°.
What's the acceleration of the bus?

Homework Equations


ΣF=m.a

The Attempt at a Solution


The first thing i thought of is air friction, but it related to speed not acceleration, and the ball is inside the bus, it would be negligible.
Nothing exept that came to my mind.

You can ignore the air resistance. Two questions:

What happens to something inside the bus that is attached to the bus?

What happens to something inside the bus that is not attached to the bus?
 
kuruman said:
You're right, air resistance is not an issue because the air moves with the bus. How about drawing a free body diagram?
Yeah, but the only forces i can think of are gravity and rope.
 
If somthing is attached
PeroK said:
You can ignore the air resistance. Two questions:

What happens to something inside the bus that is attached to the bus?

What happens to something inside the bus that is not attached to the bus?

If somthing is attached, it accelerate at the same rate as the bus.
And if it's not (ignoring friction) it would roll back.
But how does that help me?
 
Mohamed BOUCHAKOUR said:
If somthing is attached, it accelerate at the same rate as the bus.

Yes.

Mohamed BOUCHAKOUR said:
And if it's not (ignoring friction) it would roll back.

Is the ball in this case rolling back?
 
PeroK said:
Is the ball in this case rolling back?
In a way yes(the 18° angle) , but then the rope prevents it from continuing,
 
Mohamed BOUCHAKOUR said:
In a way yes(the 18° angle) , but then the rope prevents it from continuing,

What does that mean in the ground frame?

What does someone outside the bus see happen to the ball? Is it rolling/stationary/accelerating?
 
PeroK said:
What does that mean in the ground frame?

What does someone outside the bus see happen to the ball? Is it rolling/stationary/accelerating?
Accelerating
 
  • #10
Mohamed BOUCHAKOUR said:
Accelerating

So now you know all the forces on the ball. Or, at least, can calculate them.
 
  • #11
PeroK said:
So now you know all the forces on the ball. Or, at least, can calculate them.
Still can't see it...
 
  • #12
Mohamed BOUCHAKOUR said:
Still can't see it...

Have a think and draw a free-body diagram.
 
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  • #13
PeroK said:
Have a think and draw a free-body diagram.
I think I've got it, thanks for the help ✌✌
 

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