7. The net torque due to forces F1, F2 and F3 applied to a...

7. The net torque due to forces F1, F2 and F3 applied to a plate which can rotate about point O is zero. Which of the forces, when is/are removed, does not cause the net torque to change? A) F1 only B) F3 only C) F4 only D) F1 and F3 E) F4 and F3 8. The force F is applied to a plate which can rotate about point O, as shown in the figure. The plate and force F are in the plane of the page. If the torque due to the horizontal component of force F is ?x and the torque due to the vertical component of force F is ?y, what is the ratio ?x / ?y? A) 1/?5 B) 1/2 C) ?2/2 D) ?2 E) 2

Transcript

00:01 Hi, here there are two questions.

00:03 In the first question, it is given that there are many forces acting on the system.

00:07 The force f1 is acting the vertically downward direction and the force f2 is acting with a certain inclination and the perpendicular distance for the f2 is this is the one.

00:24 And when these many forces are applied on this particular triangular plane and and this plate tends to rotate about the point o.

00:33 We need to find out if we remove one particular force, the net torque will not change.

00:43 So the net torque due to the forces f1, f2, f3 applied to this plate is 0.

00:52 Which can rotate about this plate can rotate about the point o.

00:56 If we remove one particular force and the net force will not change at all.

01:02 Now let us analyze.

01:05 Now coming to the force, f1, this force f1 is acting along the axis.

01:10 So there is no perpendicular distance.

01:11 The perpendicular distance is zero.

01:13 So this force f1 will not cause any moment at all.

01:17 And this force f1 and f4 joining together will form a couple.

01:23 And the force f2 multiply with the perpendicular distance this one.

01:28 So this is causing a clockwise moment and coming to the force f3, f3 is acting along this direction therefore the perpendicular distance will be this one.

01:41 This causes an anticlockwise moment about the point o.

01:45 Therefore this f1 multiply the perpendicular distance is 0 and f2 is causing clockwise moment and f3 is causing anticlockwise moment.

01:59 Therefore, if we remove the force f1, the net dot will not change at all.

02:06 Therefore, from the given options we find that the option a is the correct answer...

Question

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