00:04Question is, a body constrained to move in the y direction is subjected to a force given
00:15by F is equal to minus 2i plus 15j plus 6k Newton. What is the work done by this force
00:24in moving the body a distance 10 meters along the y axis? a 20 joule, b 150 joule, c 160
00:37joule, d 190 joule.
00:42Yes, we have to find the work done. So, work done is calculated by the formula w is equal to
00:52F dot S. So, work done will be equal to S. The value of force is given as minus 2i
01:07plus 15j plus 6k dot
01:15displacement is given along y axis which is 10 meters. So, it is 10j because the unit vector along y
01:28axis is j.
01:31So, work done will be obtained is so minus into plus it will be minus 2 into 10 it will
01:44be 20i dot j plus 15 into 10 it will be 150j dot j plus 6 into 10 it will
01:58be 60
02:00k dot j. As we know that i dot j is equal to 0 and k dot j is also
02:13equal to 0 but j dot j is equal to 1 because the dot product of different unit vectors is
02:230
02:23because the angle between these vectors is 90. But the dot product of same unit vectors is always 1 because
02:32the angle between them is always 0. So, work done will be minus 20 as i dot j is equal
02:41to 0 into 0 plus 150 as j dot j is equal to 1 plus 60 into k dot j.
02:53So, k dot j is equal to 0 into 0 into 0. So, work done will be obtained is minus
03:0120 into 0 it will be 0. 150 into 1 it will be 150 plus 60 into 0 it will
03:07be 0.
03:08So, work done will be obtained is 150 joules. So, the correct option will be d 150 joules.
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