21.(Explanation needed for the correct answer) 22. (Explanation needed for the c

Question

21.(Explanation needed for the correct answer) 22. (Explanation needed for the correct answer) 23.(Explanation needed for the correct answer)
21-23 as seen in image above
21. A disk of known radius and rotational inertia can rotate withour friction in a horizontal plane around its fixed central axis. The disk has a cord of negligible mass wrapped around its edge. The disk is initially at rest, and the cord can be pulled to make the disk rotate. Which of the following procedures would best determine the relationship between applied torque and the resulting change Boulder: Force F to the left No acceleration in angular momentum of the disk? (A) Pulling on the cord, exerting a force of 15 N Wagon: Force F to the left for 2 s and then 25 N for 3 s, and measuring Acceleration a to the left the final angular velocity of the disk (B) For five different time intervals, pulling orn the cord, exerting a force of 15 N, and then measuring the angle through which the disk rotates in each case (C) For five different time intervals, pulling Truck: Force F to the left on the cord, exerting a force of 15 N, and then measuring the final angular velocity of the disk Acceleration a to the right 23. Each of the figures above shows a tractor attached (D) For five forces of different magnitude to an object. The tractor exerts the same constant force F on each object in every case. Which of the following is a true statement about an object and the relative magnitude of the force exerted by the object on the tractor? pulling on the cord for 5 s, and then measuring the final angular velocity of the disk 22. When object X with charge +2 uC is I m from (A) The magnitude of the force exerted by the object Y with charge-3 ?C, the magnitude ofthe force between them is F. Object Y is removed and object Z with charge -2 uC is placed 2 m from object X. What is the magnitude of the ? truck on the tractor is greatest, because the resulting motion is in the direction opposite the tractor's pull. (B) The magnitude of the force exerted by the force between objects X and Z boulder on the tractor is least, because no motion results. T-FR (A) F/2 (B) F/3 (C) F/4 (C) The magnitude of the force exerted by the wagon on the tractor is least, because the resulting motion is in the direction of the tractor's pull (D) The magnitude of the force exerted by each object on the tractor is equal, because the tractor exerts an equal force on each object.

Explanation / Answer

21. given disc of known inertia I, radius r

rotates without friction in horizontal plane

so for experimentally determining the relationship between force exerted and acceleration achieved

we need to determine the factors that are easier to measure

angular velocity is more easily measured than the rotated angle

hence pulling tghe cord with force F ( five different) will give us 5 different values of final angular velocities for t = 5 s

then angular acceleration is given by alpha = w/t

hence

graph between F and w/t will give relationship between alpha and F

hecne option D

22. Qx = 2 uC

d = 1 m

Qy = -3 uC

Force = F = kQxQy/1

F = -6k

Qz = -2 uC

d = 2 m

F' = kQxQz/4 = -4k/4 = -k = F/6

hecne option D

23. magnitude of force exerted by boulder = F

magnitude of force exerted by cart = F ( action reaction pair)

magnitude of force exerted by truck = F

hence D> the magfnitude of the force exerted by each object on tractor is equal because tractor applies equal force on each objext and these are action reacton pairs

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