Mechanics | Relativity Answers

An angular momentum of a fly wheel having a momentum of inertia of 0.125kgm^2 decreases form 3.0kgm^2/s to 2.0kgm^2/s in a period of 1.5secs.
(i) what is the average torque acting on the fly wheel during this period.
(ii) assuming a uniform angular acceleration, through how many revolution will the fly wheel have turned?

Write down expectation value of 1/r for hydrogen atom.

A special prototype model airplane of mass 400g has a control wire 8cm long attached to its body. The other end of the control line is attached to a fixed point. When the airplane flies with its wings horizontal in a horizontal circle, making one revolution every 4seconds, the control wire is elevated to 30 degrees above the horizontal. Draw a diagram showing the forces exerted on the plane and determine (i) the tension in the wire (ii) the lift on the plane ( Assume acceleration of free fall, g= 10m/s and 2=10)

A stone of mass 500g is attached to a string of length 50cm which will break if the tension in it exceeds 20N. The stone is whirled in a vertical circle, the axis of rotation being at a height of 100cm above the ground. The angular speed is very slowly increased until the string breaks. In what position is the break must likely to occur, and at what angular speed? Where will the stone hit the ground?

Explain what is meant by angular speed. Derive an expression for the force required to make a particle of mass m move in a circle of radius r with uniform angular speed w.

An object of mass 4kg moves round a circle of radius 6m with a constant speed of 12m/s. Calculate (i) the angular speed (ii) the force towards the center.

A small mass of 0.2 kg is whirled round in a horizontal circle at the end of a string of length 0.5m at a constant angular speed of 4rad/. The tension (force) in the string in Newton is?

When a stone of mass m at the end of a string is whirled in a vertical circle at a constant speed, (A) the tension (force) in the string stays constant (B) the tension is least when the stone reaches the bottom of the circle (C) the tension in the string is always mg (D) the weight mg is always the centripetal force (E) the tension is greatest when the stone is at the bottom of the circle

When a girl rides round the corner on her bicycle at a steady speed (A) there is no force when she turns (B) the force on her bicycle is only her weight when she turns (C) the centripetal force is due to the tyre friction at the ground (D) the force on the girl is always outwards (E) she stays upright (vertical)

A small mass m is suspended from one end of a vertical string and then whirled in a horizontal circle at a constant speed v. (A) The string stays vertical (B) The string becomes inclined to the vertical (C) There is no force on m except its weight (D) The angle of inclination to the vertical of the string does not depend on v (E) The centripetal force is equal to the weight mg