Confusion of circle and sphere for physics problems

In summary, the conversation discusses solving a question involving atmospheric pressure and the surface area of a sphere. The initial attempt using the surface area of the sphere resulted in an incorrect answer, but after using the projected area of a circle instead, the correct answer was obtained. The discussion also touches on the importance of considering the direction of the force when calculating pressure.
  • #1
zabachi
33
0

Homework Statement



The problem is attached

Homework Equations



P=F/A

The Attempt at a Solution



I did the question like this (got wrong answer though):

Surface area of sphere=4∏r2=4×∏×0.252
Atmospheric pressure=1.01×105

Force=1.01×105×4×∏×0.252≈80000N
Actual answer 20000N

So my friend said something about using a circle instead? I tried it and indeed got the right answer. So why do we use a circle's area instead of sphere.
 

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  • #2
Check the value of radius.
 
  • #3
i Changed the radius but the answer still reamins the same as i did the question previously itself
 
  • #4
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object.

The force is not completely perpendicular to the whole surface of hemisphere.
 
  • #5
You have to resolve the pressure force acting on each element of area of one of the hemispheres into the component in the direction that the rope is pulling. This is equivalent to using the projected area of the hemisphere times the atmospheric pressure.
 

Related to Confusion of circle and sphere for physics problems

1. What is the difference between a circle and a sphere in physics?

A circle is a two-dimensional shape that is formed by a set of points that are equidistant from a central point. It lies on a plane and has a circumference, but no depth or volume. A sphere, on the other hand, is a three-dimensional shape that is formed by rotating a circle around a central axis. It has a surface area and volume, and is often used to represent physical objects in space.

2. Why is it important to differentiate between circles and spheres in physics problems?

In physics, the properties and equations used for circles and spheres are different. Circles are used to represent planar objects, while spheres are used for three-dimensional objects. Mixing up these two shapes can lead to incorrect calculations and solutions to problems.

3. How can we tell the difference between a circle and a sphere in a physics problem?

If the problem is in a two-dimensional plane and involves objects that lie on that plane, it is most likely dealing with circles. On the other hand, if the problem involves objects that have depth or are moving in three-dimensional space, it is likely dealing with spheres. Additionally, paying attention to the units used in the problem can also help differentiate between circles and spheres.

4. Are there any real-life examples where the confusion between circles and spheres can cause problems in physics?

Yes, there are several real-life examples where mixing up circles and spheres can lead to incorrect solutions. One example is calculating the trajectory of a projectile. If the object is assumed to be a sphere instead of a circle, the trajectory will be incorrect. Another example is calculating the surface area of a pool. If the pool is mistakenly assumed to be a circle instead of a sphere, the surface area will be underestimated.

5. How can we avoid confusion between circles and spheres in physics problems?

To avoid confusion, it is important to carefully read and understand the problem before attempting to solve it. Pay attention to the wording and units, and visualize the problem to determine whether it involves circles or spheres. If in doubt, it is always helpful to draw a diagram to represent the problem and label all relevant shapes and measurements. It is also important to review and understand the equations and properties of circles and spheres before attempting to solve problems involving them.

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