13 April 2010

Mechanics

UNIT – I FORCE, WORK, POWER AND ENERGY


1. A force acting on a particle is _______ if the particle, after going through a complete round trip, returns to its initial position with the same KE as it had initially.


a) conservative b) non-conservative c) central force d) none


2. Examples of conservative forces is ________


a) gravitational force b) electrostatic force c) elastic force d) both a, b and c


3. All central forces are _________


a) conservative force b) non-conservative force c) central force d) none


4. A force acting on a particle is non-conservative if the net work by the force in a complete round trip of the particle is


a) zero b) infinity c) not zero d) none of these


5. Examples of non-conservative forces is ________


a) gravitational force b) electrostatic force c) elastic force


d) viscous force


6) The ratio of limiting friction F to the normal reaction N is defined as_________


a) coefficient of friction b) constant friction c) limiting friction d) none


7) The tangent of the angle of the inclined plane for just sliding gives the


a) coefficient of friction b) constant friction c) limiting friction d) none


8) Dimensional formula for work is a) ML-1T-2 b) M2L3T3 c) ML-1T-1 d) ML2T-2


9) ________ is the energy possessed by a body by virtue of its position or state of strain.


a) KE b) PE c) Viscous energy d) none of these


10. One horse power is a) 746watt b) 890watt c) 234watt d) 657watt


11. A body of 15kg mass is placed on a rough horizontal plane. If the coefficient of friction is 0.4, find the least horizontal force to move the body.


a) 80.2N b) 34.7N c) 12.6N d) 58.8N


Answers:
1) a 2) d 3) a 4) c 5) d 6) a 7) a 8) d 9) b 10) a 11) d


UNIT – II PROJECTILE

1. The angle of projection, for which the horizontal range and the maximum height of a projectile are equal, is


a. 45 b. θ=tan-14 c. θ=tan-1(0.25) d. none of these


2. A stone is thrown with a velocity u making an angle θ with the horizontal. The


horizontal distance covered by its fall to ground is maximum when the angle θ is equal to ___ degree.


a. 0 b. 30 c. 45 d. 90


3. A ball is thrown upwards and it returns to ground describing a parabolic path. Which of the following remains constant?


a. KE of the ball b. speed of the ball c. horizontal component of velocity d. vertical component of velocity


4. At the top of the trajectory of a projectile, the directions of its velocity and acceleration are


a) Perpendicular to each other b) parallel to each other


c) inclined to each other an angle of 45 d) anti-parallel to each other


5. Two bodies are projected at angles θ and (90 - θ) to the horizontal with the same speed. The ratio of their times of flight is


a) 1:1 b) tan θ: 1 c) 1: tan θ d) tan2 θ : 1


6. ________ is the path described by the particle.


a. range b. trajectory c. time of flight d. angle of projection


7. _______ is the angle that the direction of projection makes with the


horizontal plane through the point of projection.


a) range b) trajectory c) time of flight d) angle of projection


8. A particle is projected with a velocity 32 m/s at an angle 60 to the horizontal. What is the range on a plane inclined at 30 to the horizontal when projected up the plane?


a) 76.45m b) 45.78m c) 69.66m d) none of these


Answers:
1) b 2) c 3) c 4) a 5) b 6) b 7) d 8) c


UNIT - III Reduced Mass, Satellites and Rocket Motion

1) The principle of jet propulsion is based on


a) Newton’s third law of motion b) Newton’s law of gravitation


c) Stokes law d) None of the above


2) There is no atmosphere on moon because


a) it is closer to earth b) it revolves round the earth c) it gets light from the sun d) the escape velocity of the gas molecules is less than their root mean square velocity here.


3) The escape velocity of a projectile from the earth is approximately


a) 7km/sec b) 112km/sec c) 11.2km/sec d) 1.1km/sec


4) A small satellite is revolving near earth’s surface. Its orbital velocity


will be nearly a) 8km/sec b) 11.2km/sec c) 4km/sec d) 6km/sec


5) If ve and vo represent the escape velocity and orbital velocity of a


satellite corresponding to a circular orbit of radius R, then


a) ve = vo b) ve = vo c) ve = vo d) ve and vo are not related


6) Geo-stationary satellite is one which


a) remains stationary at a fixed height from the earth’s surface


b) revolves like other satellites but in the opposite direction of


earth’s rotation


c) revolves round the earth at a suitable height with same velocity


and in the same direction as earth does about its own axis


d) none of the above


7) An artificial satellite orbiting the earth does not fall down because the


earth’s attraction,


a) is balanced by the attraction of the moon


b) produces the necessary acceleration for its motion in a curved path


c) vanishes at such distances


d) is balanced by the viscous drag produced by the atmosphere


8) The escape velocity on the moon is _______________


a) 2.4 x 10^3 b)5.4 x 10^3 c) 8.4 x 10^3 d) none


9) The escape velocity on the sun is _______________


a) 2.4 x 10^5 b) 5.4 x 10^8 c) 6.8 x 10^5 d) none


10) If the period of the satellite in its orbit is exactly equal to the period of


rotation of the earth about its axis which is 24 hrs. Such a satellite is


known as a) synchronous satellite b) asynchronous satellite


c) ordinary satellite d) none of these


11) The rockets are normally expected to carry some load called the _________


a) pay-load b) applied load c) actual load d) none


12) The major advantage of the solid propellant rocket is __________


a) its relative simplicity in design b) its motion c) its velocity d) none


13) The unit of specific impulse is __________


a) second b) second3 c)Kgm2s-4 d) none


14) __________ is a natural satellite of our earth.


a) Venus b) Saturn c) moon d) both a and b


Answers:
1) a 2) d 3) c 4) a 5) b 6) c 7) b 8) a 9) c 10) a


11) a 12) a 13) a 14) c


UNIT - IV CONSERVATION LAWS


1. The coefficient of restitution ‘e’ for a perfectly elastic collision is


a) 1 b) 0 c) infinity d) -1


2. The coefficient of restitution ‘e’ for a perfectly inelastic collision is


a) 1 b) 0 c) infinity d) -1


3. A body of mass m collides against a wall with a velocity u and


rebounds with the same velocity. The change in momentum is


a) zero b) mv c) 2mv d) –mv


4. A bullet hits and gets embedded in a solid block resting on a


horizontal frictionless table. What is conserved?


a) Momentum alone b) KE alone c) momentum & KE both d) none of these


5. When two bodies stick together after collision, the collision is said to


be a) partially elastic b) elastic c) inelastic d) none of these


6. A ball hits the floor and rebounds after an inelastic collision. In this


case


a) the momentum of the ball just after the collision is the same as that just


before the collision.


b) the mechanical energy of the ball remains the same in the collision


c) the total momentum of the ball and the earth is conserved


d) the total energy of the ball and the earth is conserved


7. A particle at rest suddenly breaks into two fragments of equal masses


which start moving. The two will move in


a) same direction with equal velocities


b) any two directions with any velocities


c) opposite directions with unequal velocities


d) opposite directions with same velocities


8. The vector sum of the external forces acting upon a system of particles


equals zero, the total linear momentum of the system


a) remains constant b) varied c) gets a max value d) none


9. In the absence of the external force, the linear momentum of the


particle


a) remains constant b) varied c) gets a max value d) none


10. The impulse of a force is equal to the ___________ produced.


a) change in force b) change in momentum


c) change in velocities d) change in masses


11. _________ is infinitely great force acting for a very short interval of


time, such that their product is finite.


a) Viscous force b) longitudinal force c) an impulsive force


12. The study of collisions is based on the principles of __________


a) conservation of momentum b) conservation of energy


c) both a and b d) none of these


13. Elastic collisions are those in which the total KE before & after the


collisions
a) remains unchanged b) changed c) occur slightly d) none


14. If the KE is not conserved, the collisions is said to be


a) elastic b) inelastic c) both a & b d) none of these


15. The coefficient of restitution depends only on the ________ of the body


a) material b) masses c) velocities d) none


16. The coefficient of restitution for two glass balls


a) 0.2 b) 0.94 c) infinity d) 0.68


17. The value of ‘e’ lies between


a) 0 & 1 b) -1 & 0 c) -1 & 1 d) - infinity to + infinity


18. The coefficient of restitution for two lead balls


a) 0.2 b) 0.94 c) infinity d) 0.68


19. When e=1 the loss of K.E due to direct impact of two smooth spheres


is ________ a) one b) zero c) infinity d) none


20. When the vector sum of the external forces acting upon a system of


particles equals ________ the total linear momentum of the system remains constant.


a) infinite b) value c) zero d) none of these


Answers:
1) a 2) b 3) c 4) a 5) c 6) c 7) d 8) a 9) a 10) b 11) c 12) c 13) a 14) b 15) a 16) b 17) a 18) a 19) b 20) c




UNIT – V MOTION OF A RIGID BODY


1. The moment of inertia of a body does not depend upon the __________ of the body


a) angular velocity b) mass c) distribution of mass d) axis of rotation


2. If a gymnast, sitting on a rotating stool with his arms out stretched, suddenly lowers his hands


a) the angular velocity decreases b) his moment of inertia decreases


c) the angular velocity stays constant d) the angular momentum increases


3. MI of a circular disc of mass M and radius R rotating about an axis passing through its edge and perpendicular to the plane of the disc is


a) MR^2 b) 2M(R^2) c) (3/2)MR^2 d) (MR^2)/2


4. MI of a solid sphere of mass M and radius R about any tangent is


a) (2/5)MR^2 b)(7/5)MR^2 c) (2/3)MR^2 d)(5/3)MR^2


5. Angular momentum of a body is defined as the product of


a) mass and angular velocity b) centripetal force and radius


c) linear velocity and angular velocity d) moment of inertia and angular velocity


6. When the torque acting upon a system is zero, which of the following will be constant?


a) force b) linear momentum c) angular momentum d) linear impulse


7. When a steady torque is acting on a body, the body


a) continues in its state of rest or uniform motion along a straight line


b) gets linear acceleration c) gets angular acceleration


d) rotates at a constant speed


8. The rate of change of angular momentum is equal to


a) force b) angular acceleration c) torque d) moment of inertia


9. A hollow cylinder and solid cylinder having the same mass and same diameter are


released from rest simultaneously from the top of an inclined plane. Which


will reach bottom first?


a) solid cylinder b) hollow cylinder


c) both will reach the bottom together d) the one having greater density


10. A couple of 10 Nm is applied to a wheel of mass 10kg and radius of gyration 0.5m. What is the resulting angular acceleration?


a) 8 rad s-2 b) 2 rad s-2 c) 4 rad s-2 d) 13 rad s-2


11. A solid has a mass 3500 gm and radius 1.5m. Calculate MI of the sphere about a


diameter.


a) 3.15 kgm2 b) 6.15 kgm2 c) 1.15 kgm2 d) 8.15 kgm2




12. Torque has the dimensions of force times __________


a) velocity b) distance c) mass d) gravity




13. Dimensional formula for torque is


a) ML2T-2 b) ML-1T-2 c) ML-2T-2 d) M2L2T-2


Answers:
1) a 2) b 3) c 4) b 5) d 6) c 7) c 8) c 9) a 10) c 11) a 12) b 13) a