Find the magnitude of the torque

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SUMMARY

The discussion focuses on calculating the magnitude of torque about point P when a 68 lb force is applied. The initial calculation used the formula t = r X F, with r set to 4 and the sine of the angle considered. However, participants emphasized the importance of using vector notation for torque calculations, suggesting the use of the determinant expression for the cross product to obtain a vector result. The correct approach involves calculating the torque vector and then determining its magnitude through the dot product.

PREREQUISITES
  • Understanding of torque and its vector representation
  • Familiarity with the cross product in vector mathematics
  • Knowledge of trigonometric functions, specifically sine and cosine
  • Ability to perform vector calculations and dot products
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  • Study the determinant method for calculating the cross product of vectors
  • Learn about vector magnitudes and how to compute them using dot products
  • Explore torque applications in physics, particularly in rotational dynamics
  • Review trigonometric identities and their applications in vector calculations
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Students studying physics, particularly those focusing on mechanics and torque calculations, as well as educators looking for effective teaching methods in vector mathematics.

jonnejon
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Homework Statement


Find the magnitude of the torque about P if a 68 lb force is applied as shown. Give your answer correct to the nearest integer.
12-4-40.gif

Homework Equations


t=r X F

The Attempt at a Solution


t = (4)(68)(sin30)
= 136
 
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Don't you want to consider the distance at which it is acting is 4*√2 ?

At the point of interaction then the ⊥ component of F looks to me like F*Cos15°
 


jonnejon said:

Homework Statement


Find the magnitude of the torque about P if a 68 lb force is applied as shown. Give your answer correct to the nearest integer.
12-4-40.gif



Homework Equations


t=r X F


The Attempt at a Solution


t = (4)(68)(sin30)
= 136


You wrote what must have been intended to be a vector equation for the torque, t = r x F, because the cross product only makes sense if t, r, and F are all expressed as vectors. But then you proceeded to do a scalar calculation. Why not make your torque calculation in vector form using the determinant expression for the cross product and giving the resulting torque as a vector? Then if you need the magnitude of that vector, dot it with itself and take the square root of the result.
 

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