In a screw jack, the effort required to lift the load is given by (where W = Load lifted, α = Helix angle, and φ = Angle of friction.)
P = W tan (α - φ)
P = W tan (α + φ)
P = W tan (φ - α)
P = W cos (α + φ)
Correct Answer :
B. P = W tan (α + φ)
Related Questions
Whenever a force acts on a body and the body undergoes a displacement, then
Work is said to be done
Power is being transmitted
Body has kinetic energy of translation
None of these
According to Newton's first law of motion,
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
None of the above
In determining stresses in frames by methods of sections, the frame is divided into two parts by an imaginary section drawn in such a way as not to cut more than
Two members with unknown forces of the frame
Three members with unknown forces of the frame
Four members with unknown forces of the frame
Three members with known forces of the frame
The centre of gravity of a triangle lies at the point of
Concurrence of the medians
Intersection of its altitudes
Intersection of bisector of angles
Intersection of diagonals
Lami's theorem states that
Three forces acting at a point will be in equilibrium
Three forces acting at a point can be represented by a triangle, each side being proportional to force
If three forces acting upon a particle are represented in magnitude and direction by the sides of a triangle, taken in order, they will be in equilibrium
If three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two
The principle of transmissibility of forces states that, when a force acts upon a body, its effect is
Same at every point on its line of action
Different at different points on its line of action
Minimum, if it acts at the centre of gravity of the body
Maximum, if it acts at the centre of gravity of the body
The overturning of a vehicle on a level circular path can be avoided if the velocity of vehicle is __________ √(gra/h)
Less than
Greater than
Equal to
None of these
A framed structure is imperfect, if the numbers of members are __________ (2j - 3).
Equal to
Less than
Greater than
Either (B) or (C)
Forces are called concurrent when their lines of action meet in
One point
Two points
Plane
Perpendicular planes
A block of mass m1, placed on an inclined smooth plane is connected by a light string passing over a smooth pulley to mass m2, which moves vertically downwards as shown in the below figure. The tension in the string is 
m1/m2
m1. g. sin α
m1.m2/m1 + m2
m1. m2.g (1 + sin α)/(m1 + m2)
The centre of percussion of a solid cylinder of radius r resting on a horizontal plane will be
r/2
2r/3
r/A
3r/2
A flywheel on a motor goes from rest to 1000 rpm in 6 sec. The number of revolutions made is nearly equal to
25
50
100
250
The moment of inertia of a solid cylinder of mass m, radius r and length l about the longitudinal axis or polar axis is
mr2/2
mr2/4
mr2/6
mr2/8
The frequency of oscillation of a compound pendulum is (where kG = Radius of gyration about the centroidal axis, and h = Distance between the point of suspension and C.G. of the body.)
2π. √(gh/kG² + h²)
2π. √(kG² + h²/gh)
1/2π. √(gh/kG² + h²)
1/2π. √(kG² + h²/gh)
Centre of gravity of a thin hollow cone lies on the axis at a height of
One-fourth of the total height above base
One-third of the total height above base
One-half of the total height above base
Three-eighth of the total height above the base
The moment of inertia of a thin spherical shell of mass m and radius r, about its diameter is
mr2/3
2mr2/3
2mr2/5
3mr2/5
If a number of forces are acting at a point, their resultant will be inclined at an angle θ with the horizontal, such that
tanθ = ΣH/ΣV
tanθ = ΣV/ΣH
tanθ = ΣV × ΣH
tanθ = √(ΣV + ΣH)
The rate of doing work is known as
Potential energy
Kinetic energy
Power
None of these
Moment of inertia of a triangular section of base (b) and height (h) about an axis passing through its C.G. and parallel to the base, is
bh3/4
bh3/8
bh3/12
bh3/36
Which of the following is an equation of linear motion? (where, u and v = Initial and final velocity of the body, a = Acceleration of the body, and s = Displacement of the body in time t seconds.)
v = u + a.t
s = u.t + ½ a.t2
v2 = u2 + 2a.s
All of these
In a framed structure, as shown in the below figure, the forces in the members AB and BC are respectively 
√3. W (tensile) and 2W (compressive)
2W (tensile) and √3. W (compressive)
2√3. W (tensile) and 2√3. W (compressive)
None of the above
The unit of energy in S.I. units is
Dyne
Watt
kg-m
Joule
A weight of 1000 N can be lifted by an effort of 80 N. If the velocity ratio is 20, the machine is
Reversible
Non-reversible
Ideal
None of these
The three forces of 100 N, 200 N and 300 N have their lines of action parallel to each other but act in the opposite directions. These forces are known as
Coplanar concurrent forces
Coplanar non-concurrent forces
Like parallel forces
Unlike parallel forces
The velocity ratio of a differential wheel and axle with D as the diameter of effort wheel and d1 and d2 as the diameters of larger and smaller axles respectively, is
D/(d₁ + d₂)
D/(d₁ - d₂)
2D/(d₁ + d₂)
2D/(d₁ - d₂)
Moment of inertia of a hollow circular section, as shown in the below figure about an axis perpendicular to the section, is __________ than that about X-X axis. 
Two times
Same
Half
None of these
A force is completely defined when we specify
Magnitude
Direction
Point of application
All of the above
The force induced in the string BC due to the load W as shown in the below figure is 
W sinθ
W cosθ
W tanθ
W cotθ
Two coplanar couples having equal and opposite moments
Balance each other
Produce a couple and an unbalanced force
Are equivalent
Cannot balance each other
The skidding away of the vehicle on a level circular path can be avoided if the force of friction between the wheels and the ground is __________ the centrifugal force.
Less than
Greater than
Equal to
None of these