Numerical Problem No. 2.12 (Vectors and Equilibrium) Physics HSSC - I (Class -11) (Punjab Curriculum and Text Board, Lahore) With Verified Answers

The torque or turning effect of force about a given point is given by r x F where r is the vector from the given point to the point of application of F. Consider a force F = - 3 `\hat {i}` + `\hat {j}` +5`\hat {k}` (newton) acting on the point 7`\hat {i}` + 3 `\hat {j}` + `\hat {k}` (m). What is the torque in N m about the origin?

(Ans: 14`\hat {i}` -38 `\hat {j}` +16`\hat {k}` Nm ]

Given:

Force = `\vec {F}` = -3`\hat {i}` + `\hat {j}` + 5`\hat {k}` Newton

Position Vector = `\vec {r}` = 7`\hat {i}` + 3`\hat {j}` + `\hat {k}`  meters

To Find:

Torque = T = ?

Solution: 

We know that 

T = `\vec {r}` ｘ `\vec {F}` 

by putting values

T = `\vec {r}` ｘ `\vec {F}`  = (-3`\hat {i}` + `\hat {j}` + 5`\hat {k}`)ｘ (7`\hat {i}` + 3`\hat {j}` + `\hat {k}`)  Nm

Cross product of two vectors can be solved by writing determinant method and then expanding

T = `\vec {r}` ｘ `\vec {F}`  = `\hat {i}`(15 - 1) - `\hat {j}` (35 + 3) + `\hat {i}`(7 +9)

T = `\vec {r}` ｘ `\vec {F}`  = 14`\hat {i}` - 38`\hat {j}` + 16 `\hat {i}` Nm  ----- Ans

************************************

************************************

Numerical Problem 2.12
⇑

List of 11th Physics Numerical Problems of Chapter - 2

⇑

Numerical Problem 2.11  ⇚   11th Physics Main Content List    ⇛ Numerical Problem 2.13

************************************

Shortcut Links For 

1. National MDCAT, ECAT, JOB EXAM Physics MCQs Preparation (New) 
2. Physics (New) 11th Class SLO Based Notes
3. Physics (New) 11th class MCQs Quizzes All Units
4. Physics (New) 12th Class SLO Based Notes
5. Physics (New) 12th class MCQs Quizzes All Units

1. Website for School and College Level Physics   

(https://askrarequiz.blogspot.com)

2. Website for School and College Level Mathematics  

(https://askraremaths.blogspot.com)

3. Website for Single National Curriculum Pakistan - All Subjects Notes 

(https://askrareclassnotes.blogspot.com/)

© 2022-Onwards by Academic Skills and Knowledge (ASK)     

Note:  Write me in the comment box below for any query and also Share this information with your class-fellows and friends.