The condition for a lifting machine to be reversible is that its efficiency should be
Less than 50%
More than 50%
More than 66.67%
Equal to 100%
Correct Answer :
B. More than 50%
Related Questions
Two balls of masses 3 kg and 6 kg are moving with velocities of 4 m/sec and 1 m/sec respectively, towards each other along the line of their centers. After impact the 3 kg ball comes to rest. This can happen only if the coefficient of restitution between the balls is
2/3
1/5
3/5
1/3
If the radius of the earth is 600 km the height of a mountain above sea level at the top of which a beat seconds pendulum at sea level, looses 27 seconds a day, is
500 metres
1000 metres
1500 metres
2000 metres
In a lifting machine with efficiency 60%, an effort of 200 N is required to raise a load of 6 kN. The velocity ratio of the machine is
30
50
60
80
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)
The C.G. of a right circular cone lies on its axis of symmetry at a height of
h/2
h/3
h/4
h/5
In SI units, the units of force and energy are respectively
Newton and watt
Dyne and erg
Newton and joule
kg wt and joule
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
The motion of a particle is described by the relation x = t2- 10t + 30, where x is in metres and t in seconds. The total distance travelled by the particle from t = 0 to t = 10 seconds would be
Zero
30 m
50 m
60 m
If two forces P and Q (P > Q) act on the same straight line but in opposite direction, their resultant, is
P + Q
P/Q
Q/P
P - Q
A car goes round a curve of radius 100 m at 25 m/sec. The angle to the horizontal at which the road must be banked to prevent sideways friction on the car wheels is tan1 x, where x is (Assume g = 10 m/sec²)
3/8
1/2
9/5
5/8
If α is the angular acceleration of a compound pendulum whose angular displacement is θ, the frequency of the motion is
2π √(α/θ)
(1/2π) √(α/θ)
4π √(α/θ)
2π √(α - θ)
A vehicle weighing w kg is to run on a circular curve of radius r. If the height of its centre of gravity above the road level is h and the distance between the centres of wheels is 2a, the maximum velocity, in order to avoid over turning, will be
gra/h
√(gra/h)
3√(gra/h)
4√(gra/h)
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
Angular acceleration of a particle may be expressed as
Radians/sec2
Degrees/sec2
Revolutions/sec
All the above
Instantaneous center is at infinity when the angular velocity is
Constant
Zero
Maximum
Minimum
From a circular plate of a diameter 6 cm is cut out a circle whose diameter is equal to the radius of the plate. The C.G. of the remainder from the centre of circular plate is at a distance of
2.0 cm
1.5 cm
1.0 cm
0.5 cm
A glass ball is shot to hit a wall from a point on a smooth floor. If the ball returns back to the point of projection in twice the time taken in reaching the wall, the coefficient of restitution between the glass ball and the wall is
0.25
0.33
0.40
0.50
A simple pendulum of length 1 has an energy E when its amplitude is A. If its amplitude is increased to 2 A, the energy becomes
E
E/2
2E
4E
M.I. of a thin ring (external diameter D, internal diameter d) about an axis perpendicular to the plane of the ring, is
π/64 (D4 + d4)
π/32 (D4 - d4)
π/32 (D4 + d4)
π/32 (D4 × d4)
A point subjected to a number of forces will be in equilibrium, if
Sum of resolved parts in any two directions at right angles, are both zero
Algebraic sum of the forces is zero
Two resolved parts in any two directions at right angles are equal
Algebraic sum of the moments of the forces about the point is zero
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
One Joule is equivalent to
9.81 Newton metre
1 Newton metre
1 kg wt metre
1 dyne metre
The centre of gravity of the trapezium as shown in below figure from the side is at a distance of
(h/3) × [(b + 2a)/(b + a)]
(h/3) × [(2b + a)/(b + a)]
(h/2) × [(b + 2a)/(b + a)]
(h/2) × [(2b + a)/(b + a)]
If two forces each equal to T in magnitude act at right angles, their effect may be neutralised by a third force acting along their bisector in opposite direction whose magnitude will be
2 T
1/2 T
√2 T
3 T
Select the correct statement
The body centrode rolls on the space centrode
The space centrode rolls on the body centrode
Both body and space centrodes may role on each other
The body centrode never touches space centrode
The reaction at the support D of the continuous beam ABCD, hinged at two points shown in below figure is 
1.6 t
1.6 t ↓
0.5 t
0.5 t ↓
When a body in equilibrium undergoes an infinitely small displacement, work imagined to be done, is known as
Imaginary work
Negative work
Virtual work
None of these
A rod 5 m in length is moving in a vertical plane. When it is inclined at 60° to horizontal, its lower end is moving horizontally at 3 m/sec and upper end is moving in vertical direction. The velocity of its upper end, is
0.5 m/sec
1.0 m/sec
1.5 m/sec
2.5 m/sec
The resultant of two forces P and Q is R. If Q is doubled, the new resultant is perpendicular to P. Then,
P = R
Q = R
P = Q
None of the above is correct
Pick up the incorrect statement from the following. In a simple harmonic motion
Velocity is maximum at its mean position
Velocity is minimum at the end of the stroke
Acceleration is minimum at the end of the stroke
Acceleration is zero at the mean position