Need help determining whether to use cosine or sine

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In summary: The sine of the angle is the opposite side divided by the hypotenuse, and the cosine is the adjacent side divided by the hypotenuse. In summary, when solving physics problems involving angles, use sine or cosine depending on whether the force in question is the opposite or adjacent side of the triangle formed by the weight as the hypotenuse.
  • #1
physicsnoob145
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I'm having trouble understanding when to use sine or cosine in my physics problems

for example I got this from one of the lectures off youtube
and I know why they are using sine and cos because it is at an angle but I'm rotating the angle to understand why it is mgcosbeta and why the other is mgsinbeta and not the other way around

could someone explain to me why it is mgcosbetahttp://img213.imageshack.us/img213/8798/91559741.png
 
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  • #2
physicsnoob145 said:
I'm having trouble understanding when to use sine or cosine in my physics problems

for example I got this from one of the lectures off youtube
and I know why they are using sine and cos because it is at an angle but I'm rotating the angle to understand why it is mgcosbeta and why the other is mgsinbeta and not the other way around

could someone explain to me why it is mgcosbeta
Visualize what it looks like when the angle is set to 0. One will be 0 and the other will be mg. The one that is 0 is sin and the one that is mg is cos. That will always work.
 
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  • #3
It helps to understand this if you construct a triangle with mg as the hypotenuse, then it becomes clear when to use sin or cosine.
 

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  • #4
rcgldr said:
It helps to understand this if you construct a triangle with mg as the hypotenuse, then it becomes clear when to use sin or cosine.

thank you it is a little clearer now
 
  • #5
Just as rcgldr has shown the weight must always be the hypotenuse as it is largest force acting.
 

FAQ: Need help determining whether to use cosine or sine

What is the difference between cosine and sine?

Cosine and sine are both trigonometric functions used in mathematics. The main difference between them is that cosine measures the horizontal distance from the origin to a point on the unit circle, while sine measures the vertical distance from the origin to the same point.

When should I use cosine?

Cosine is typically used when working with angles and triangles, as it relates the length of the adjacent side to the hypotenuse in a right triangle. It is also useful in physics and engineering for calculating forces and oscillations.

When should I use sine?

Sine is often used in geometry and trigonometry to measure the length of the opposite side in a right triangle. It is also used in physics and engineering for calculating harmonic motion and waves.

Can I use either cosine or sine in any situation?

While cosine and sine are often used interchangeably, they are not always interchangeable. It depends on the specific problem you are trying to solve and the information given. It is important to understand the difference between the two and when to use each one.

Is there a specific formula for determining when to use cosine or sine?

There is no specific formula for determining when to use cosine or sine. It is important to understand the concepts behind each function and the problem at hand in order to determine which one is most appropriate to use.

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