A uniform rod of length L and weight WR is suspended as shown in the accompanying figure. A weights W is added to the end of the rod. The rod rests in horizontal position and is hinged at O. The support wire is at an angle θ to the rod. What is the tension T in the wire?
The forces on rod hinged at O, which cause torque about O are as shown.
Since net torque on rod about hinge at O is zero
Moment of inertia of a disc object OO' is :
(by perpendicular axis theorem)
by applying parallel axis theorem
The correct answer is:
A uniform circular disc placed on a horizontal rough surface has initially a velocity v0 and an angular velocity ω0 as shown in the figure :
The disc comes to rest after moving some distance in the direction of motion. Then
The correct answer is: r/2
The moment of inertia of a door of mass m, length 2ℓ and width ℓ about its longer side is :
Using parallel axis theorem : IAD = ICM + ML2
I (about AD)
The correct answer is:
Three identical uniform rods, each of length ℓ, are joined to form a rigid equilateral triangle. Its radius of gyration about an axis passing through a corner and perpendicular to the plane of the triangle is :
MI of the system w.r.t. an axis ⊥ to plane and passing through one corner
Now, the radius of gyration is
The correct answer is:
A wheel is rolling uniformly along a level road (see fig.) The speed of translational motion of the wheel axis is v. What are the speed of the points A and B on the wheel rim relative to the road at the instant shown in the fig?
The correct answer is: VA = 0, VB = 2V
A uniform cube of side a and mass m rests on a rough horizontal table. A horizontal force mn is applied normal to one of the faces at a point that is directly below the centre of face, at a height 3a/4 above the base. The minimum value of F for which the cube begins to tilt about the edge is? (Assume that the cube does not slide).
Taking moments abut point O :
Moment of N (normal reaction) and f (force of friction) are zero. In critical case normal will pass through O. To tip about the edge, moment of F should be greater than moment of mg or,
The correct answer is:
A thin wire of length L and uniform density ρ is bent into a circular loop with centre at O as shown. The moment of inertia of the loop about the axis XX' is :
(by parallel axis theorem)
by putting value of m and t we get,
The correct answer is:
A particle performs uniform circular motion with an angular momentum L. If the frequency of particle’s motion is doubled and its kinetic energy is halved, the angular momentum becomes :
Kinetic energy
The correct answer is: L/4
Three rings each of mass m and radius r are so placed that they touch each other. The radius of gyration of the system about the axis as shown in the figure is :
I = I1 + I2 + I3
Moment of inertia = 3mk2 where k is radius of gyration.
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