Using radians to discover the lengths of geometric shapes (circles)

In summary, the conversation discusses a question about finding the inner angles of two wheels in a geometry problem. The solution involves extending one of the radii to form a rectangle and using trigonometric functions to find the missing angle. The final answer is 125cm for the major arc length.
  • #1
Elihu5991
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Homework Statement


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Homework Equations


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The Attempt at a Solution


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This is my brothers maths homework. He normally doesn't use online methods to request help and this is his first time.
 

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  • #2
Welcome to the Physics Forums.

So what's your question? We can't just do your homework for you.
 
  • #3
radians question

sorry about that, if forgot to state my problem.
i was wondering how to get the inner angles of the big and small wheel.
i've been able to get 'alpha' and 'phi' but i don't know how to get 'theta' on the big wheel.
if you can explain how i can get that then i'll be able to get the smaller wheel angle and then find the major arc lengths of both wheels.
 
  • #4
so first notice the part of band between the two wheels touches tangentially to both that means the radii that touch it both have measure pi/2 and are in fact parallel to one another.

if you extend the 6 cm radius a bit to 16 cm then you have a rectangle containing a right triangle with sides X cm, 10 cm and hypotenuse 26 cm. You can then compute its angles and go from there.

I didn't 21.49 cm for X. I got a nice integer number.
 
  • #5
Thanks I got the answer of 125cm which I checked in the back of the answers and is right. The way you explained it helped.
 

FAQ: Using radians to discover the lengths of geometric shapes (circles)

1. How do radians differ from degrees in measuring angles?

Radians and degrees are two different units used to measure angles. While degrees are based on the concept of dividing a circle into 360 equal parts, radians are based on dividing a circle into 2π (approximately 6.28) equal parts. Radians are often used in mathematical calculations involving circles and trigonometric functions.

2. How can radians be used to find the length of a circle's arc?

To find the length of a circle's arc using radians, you can use the formula S = rθ, where S is the arc length, r is the radius of the circle, and θ is the angle in radians. Simply plug in the values and solve for S.

3. Can radians be used to find the perimeter of a circle?

Yes, radians can be used to find the perimeter of a circle. The perimeter of a circle is also known as its circumference, which can be calculated using the formula C = 2πr, where C is the circumference and r is the radius of the circle. Since π is equal to half of a circle's circumference divided by its radius, we can also express this formula as C = πd, where d is the diameter of the circle. Therefore, radians are an essential part of calculating the perimeter of a circle.

4. How can radians be used to find the area of a sector?

To find the area of a sector using radians, you can use the formula A = 1/2r²θ, where A is the area, r is the radius of the circle, and θ is the angle in radians. This formula is derived from the fact that the area of a sector is equal to the area of the corresponding circle multiplied by the fraction of the circle's circumference represented by the sector's angle.

5. Can radians be used to measure angles in other geometric shapes besides circles?

While radians are most commonly used to measure angles in circles, they can also be used to measure angles in other geometric shapes, such as triangles and polygons. This is because the concept of dividing a circle into equal parts can also be applied to other regular polygons. However, degrees are still the preferred unit for measuring angles in most geometric shapes.

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