A circular disc rotates at n rpm. The angular velocity of a circular ring of same mass and radius as the disc and to have the same angular momentum is
n rpm
n/2 rpm
n/4 rpm
2n rpm
Correct Answer :
B. n/2 rpm
Related Questions
The unit of rotational inertia of a body in C.G.S system is
cm4
kg.cm²
gm.cm²
gm.cm3
A weight of 100 kg is supported by a string whose ends are attached to pegs A and B at the same level shown in below figure. The tension in the string is 
50 kg
75 kg
100 kg
120 kg
Two forces act an angle of 120°. If the greater force is 50 kg and their resultant is perpendicular to the smaller force, the smaller force is
20 kg
25 kg
30 kg
35 kg
The ratio of the reactions RA and RB of a simply supported beam shown in below figure is 
0.50
0.40
0.67
1.00
A particle of mass 2 kg executes simple harmonic motion of frequency 6/71 Hz and amplitude 0.25 m. Its maximum kinetic energy is
4.5 J
9.0 J
12.0 J
18.0 J
One Newton is equivalent to
1 kg. wt
9.81 kg. wt
981 dyne
1/9.81 kg. wt
If the velocity of projection is 4 m/sec and the angle of projection is α°, the maximum height of the projectile from a horizontal plane, is
u² cos² α/2g
u² sin² α/2g
u² tan² α/2g
u² sin 2α/2g
A disc of mass 4 kg, radius 0.5 m and moment of inertia 3 kgm² rolls on a horizontal surface so that its center moves with speed 5 m/see. Kinetic energy of the disc is
50 J
150 J
200 J
400 J
Two particles have been projected at angles 64° and 45° to the horizontal. If the velocity of projection of first is 10 m/sec, the velocity of projection of the other for equal horizontal ranges is
9.3 m/sec
8.3 m/sec
7.3 m/sec
6.3 m/sec
Periodic time of a particle moving with simple harmonic motion is the time taken by the particle for
Half oscillation
Quarter oscillation
Complete oscillation
None of these
A Seconds pendulum executes
0.5 beat per second
1.0 beat per second
2.0 beats per second
2.5 beats per second
Newtons Law of Motion is:
Everybody continues in its state of rest or of uniform motion in a straight line, unless it is acted upon by some external force
The rate of change of momentum is directly proportional to the impressed force, and takes place in the same direction, in which the force acts
To every action, there is always an equal and opposite reaction
All the above
The phenomenon of collision of two elastic bodies takes place because bodies
Immediately after collision come momentarily to rest
Tend to compress each other till they are compressed maximum possible
Attempt to regain its original shape due to their elasticities
All the above
If the gravitational acceleration at any place is doubled, the weight of a body, will
Be reduced to half
Be doubled
Not be affected
None of these
Engineer's units of force, is
Newton in absolute units
Dyne in absolute units
Newton and dyne in absolute units
All the above
A circular disc rotates at n rpm. The angular velocity of a circular ring of same mass and radius as the disc and to have the same angular momentum is
n rpm
n/2 rpm
n/4 rpm
2n rpm
To attain the synchronous orbit, the launch of a satellite, is done from a place
On equator
On 30° latitude
On 45° latitude
On the poles
Maximum efficiency of a screw jack for the angle of friction θ, is
sin θ/(1 + sin θ)
(1 - sin θ)/sin θ
(1 + sin θ)/(1 - sin θ)
(1 - sin θ)/(1 + sin θ)
If two forces are in equilibrium, then the forces must (i) Be equal in magnitude (ii) Be opposite in sense (iii) Act along the same line The correct answer is
(i) and (ii)
(i) and (iii)
Only (i)
All (i), (ii) and (iii)
The moment of inertia of the shaded portion of the area shown in below figure about the X-axis, is
229.34 cm4
329.34 cm4
429.34 cm4
529.34 cm4
The centre of gravity of a trapezoidal dam section whose top width is a, bottom width is band the vertical side is a, from its vertical face is
(a² + ab + b²)/3 (a + b)
(b² + bc + c²)/3 (b + c)
(a² + ab + c²)/3 (a + c)
None of these
A satellite moves in its orbit around the earth due to
Gravitational force
Centripetal force
Centrifugal force
None of these
A body of weight 14 g appears to weight 13 g when weighed by a spring balance in a moving lift. The acceleration of the lift at that moment was
0.5 m/sec2
0.7 m/sec2
1 m/sec2
1 cm/sec2
The resultant of two forces acting at right angles is √34 kg and acting at 60° is 70 kg. The forces are
1 kg and 4 kg
2 kg and 3 kg
√3 kg and √5 kg
3 kg and 5 kg
Parallelogram Law of Forces states, if two forces acting simultaneously on a particle be represented in magnitude and direction by two adjacent sides of a parallelogram, their resultant may be represented in magnitude and direction by
Its longer side
Its shorter side
The diagonal of the parallelogram which does not pass through the point of intersection of the forces
The diagonal of the parallelogram which passes through the point of intersection of the forces
The potential energy of a particle falling through a straight shaft drilled through the earth (assumed homogenous and spherical) is proportional to
log r
r
r²
1/r Where r is the distance of the particle from centre of the earth
The condition of equilibrium for any system of forces in a plane is
That polygon of forces must close
That resultant couple must be zero
Both (A) and (B)
None of the above
A marble ball is rolled on a smooth floor of a room to hit a wall. If the time taken by the ball in returning to the point of projection is twice the time taken in reaching the wall, the coefficient of restitution between the ball and the wall, is
0.25
0.50
0.75
1.0
One end of a light string 4 m in length is fixed to a point on a smooth wall and the other end fastened to a point on the surface of a smooth sphere of diameter 2.25 m and of weight 100 kg. The tension in the string is
17.5 kg
19.5 kg
22.5 kg
25 kg
A ball is dropped from a height of 16 m on a horizontal floor. If it rebounds to a height of 9 m after striking the floor, the coefficient of restitution between ball and floor is
1/4
2/3
3/4
4/3