The torque of force F=(2i-3j+4k)N acting at the point r=(3i+2j+3k)m about the origin be

Physics class 11th mcqs  Mdcat physics mcqs solution  First year physics mcqs  11 class physics mcqs solution

Transcript

00:00Question says, the torque of the force F is equal to 2i minus 3j plus 4k newton acting

00:15at the point R is equal to 3i plus 2j plus 3k meters about the origin will be A 6i minus

00:296j plus 12k, B 17i minus 6j minus 13k, C minus 6i plus 6j minus 12k, D minus 17i plus 6j

00:46plus 13k. As we have to find torque is, torque is the cross product of position vector and

01:03force is torque is equal to R cross F. So, by using determinate form, first we will write

01:22i, j and k, then we will put the values of R is the values of R are 3i plus 2j plus 3k.

01:39So, the value of R with i is 3, with j is 2 and with k is 3. Now, we will put the values

01:53of force, the value of force along i is 2, along j is minus 3 and along k is plus 4. So, first

02:11of all, we will take i, when we will take i, then we will neglect the column of i. So, we

02:23will multiply 2 with 4 and minus 3 with plus 3. So, 2 for the 8, this minus is our formula.

02:34minus 3 into 3, it will be minus 9. So, break it over. Now, we will take j, so we will give

02:48minus here. So, minus j into, when we will take j, then we will neglect the column of j, then

03:01we will multiply 3 with 4 and 2 with 3. So, 3 for the 12 minus 2, 3 the 6. Now, we will take

03:16k. When we will take k, then we will neglect this column, then we will multiply 3 with minus

03:243 and 2 with plus 2. So, 3 3 the minus 9. This minus is our formula. So, 2 to the 4. So, torque

03:41will be obtained is i into 8, minus into minus, it will be plus 9, minus j, plus 12 minus 6,

03:57it will be plus 6, plus k, minus 9, minus 4, it will be minus 13. So, torque will be obtained

04:15is 8 plus 9, it will be plus 9, it will be plus 8 plus 9, it will be plus 9, it will be plus

04:31k into 13, it will be 13 k. So, torque is obtained is 17 i minus 6 j minus 13 k. So, the correct

04:43option will be b, 17 i minus 6 j minus 13 k.