Thursday, February 16, 2012

mechanics test questions

Question 1
A ball is thrown vertically upwards with a velocity u from top of a tower. It strikes the ground with a velocity 3u. The time taken by the ball to reach the ground is given by
(a) u/g
(b) 2u/g
(c) 3u/g
(d) 4u/g

Question 2
A body slides down an inclined plane of inclination . The coefficient of friction down the plane varies in the direct proportion to the distance moved down the plane(=kx). The body will move down the plane with
(a) constant acceleration =gsin
(b) constant acceleration =(gsin-gcos)
(c) constant retardation =(gcos-gsin)
(d) variable acceleration that first decreases from gsin to zero and that becomes negative.

Question 3
A escalator is moving downwards with a uniform speed u. A man of mass m is running upwards on it at a uniform speed v. If the height of escalator is h, the work done by man in going up the escalator is
(a) zero
(b) mgh
(c) mghu/(v-u)
(d) mghv/(v-u)

Question 4
A particle moves in a circular orbit with a uniform angular speed. However , the plane of the circular orbit is itself rotating at a constant angular speed. We may then say that
(a) the angular velocity as well as angular acceleration of particle are both constant.
(b) neither the angular velocity nor the angular acceleration of the particle are constant.
(c) the angular velocity of the particle varies but its angular acceleration is constant.
(d) the angular velocity of the particle remains constant but the angular acceleration varies.
 
Question 5
Two objects of mass m and 4m are at rest at infinite separation. They move towards each other under mutual gravitational attraction. Then at separation r, which one of the following is true.
(a) the total energy of the system is not zero
(b) the force between them is not zero
(c) the center of mass of the system is at rest
(d) all the above are true

Answer
1. b
2. d
3. d
4. c
5. d
 
Multiple choice question with one or more answer

1. Which of these is true of a conservative force?
a. Workdone between two points is independent of the path
b. Workdone in a closed loop is zero
c. if the workdone by the conservative is positive,its potential energy increases
d. None of the these

2.A particle is acted upon by a force of costant magnitude which is always perpendicular to the velocity of the particle.The motion of the particle takes place in a plane.it follows that
a. velocity is constant
b. accelerattion is constant
c. KE is constant
d. Particle moves in a circular path

3. A package is dropped out of airplane in a level flight.If air resistance could be neglected.which of these is true
a. Package will follow a parabolic path with respect to a observer on the groud
b Package will follow a vertically straight line path with respect to the observer in the plane.
c.Package will follow a vertically straight line path with respect to a observer on the groud
b Package will follow a parabolic path with respect to the observer in the plane.


4.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.
Which of the followings is true
a.The strings stays vertical
b.The string becomes inclined to the vertical.
c.There is no force on mass m except its weight
d.The angle of inclination of the string does not depend on the v
e.The centripetal force on m is mg

5.A IITJEE text book of mass M rests flat on a horizontal table of mass m placed on the ground.Let RX->Y be the constant force exerted by the body x on body Y.Which of the following is true for the forces Rground->table and Rtable->ground
a. It is action and reaction pair
b. have equal magnitude
c. Opposite direction
d.have resultant zero


6.The tension in cable supporting an elevator is equal to th weight of the elevetor.The elevator may be
a. going up with incresing speed
b. going down with increasing speed
c. going up with uniform speed
d. going down with uniform speed.


7 A simple pendulum consists of a mass attached to a light string l. if the system is oscillating through small angles which of the following is true
a.The freqiency is independent of the acceleration due to gravity g
b.The period depends on the amplitude of the ocsillation
c.the period is independent of mass m
d. the period is independent of lenght l


8.A ball is thrown into the air with an intial speed u.The time interval taken for the ball to rise to its maximum height is t1.The time interval taken for the ball to fall back from this maximum height is t2.Under real life condition,which of the following is satisfied
a.t2 > t2
b t2 < t2
c. t2=t2
d. t1 > t2 if u is great enough


9. Let v and a denote the velolcity and acceleratio respectivly of the particle in one dimension motion.
a.the speed of the particle decreases when v.a <0
b. the speed of the particle decreases when v.a >0
c.the speed of the particle increases when v.a=0
d. the speed of the particle decreases when |v|<|a|

10. A refrence frame attached to the earth
a.is an inertial frame by defination
b.cannot be inertial frame as earth is resolving around the sun
c.is an intertial frame because Newton's law are applicable in this frame
d.cannot be intertial frame because earth is rotating about its own axis


Solutions
1.a,b
2.c,d
3.a,b
4. b
5. a,b,c,d
6. c,d
7. c
8 a
9 a
10 b,d  




Multiple choice question with one or more answer
1. A block of mAss M is moving with a velocity v on straight surface.What is the shortest distance and shortest time in which the block can be stopped if μ is coefficent of friction
a.v2/2μg,v/μg
b. v2/μg,v/μg
c.v2/2Mg,v/μg
d none of the above


2.A horizontal force of F N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is μ. The weight of the block is
a.μF
b. F(1+μ)
c. F/μ
d none of these


3.Consider the following two statements.
STATEMENT 1 Linear momentum of a system of particles is zero.
STATEMENT 2 Kinetic energy of system of particles is zero.
(A) A does not imply B and B does not imply A.
(B) A implies B but B does not imply A
(C) A does not imply B but b implies A’
(D) A implies B and B implies A.


4.The Position vector of the center of mass of uniform semi circular ring of radius R and Mass M whose center coincided with the origin
a.r=(2R/π)j
b.r=(R/π)j
c.r=(4R/π)j
d. none of the these

5.A body is sliding down a rough inclined plane of angle of inclination θ for which coefficent of friction varies with distance y as μ(y)=Ky where K is constant.Here y is the distance moved by the body down the plane.The net force on the body is zero at A.Find the value of constant K
a. tanθ/A
b. Acotθ
c. cotθ/A
d. A tanθ

6.Chosse the correct option
a.if Workdone by the conservative force is positive then Potential energy decreases
b. Rate of change of momentum of many particles system is proportional to net external force on the system
c.The workdone by the conservative force in closed loop is zero
d. None of the above

7.Two electrons(e) are the at the point (-a,0) and (a,0).Their mass is m.They are released from rest.The acceleration of the center of mass of the system when the electron at 4a distance apart
a. e2/64mπε0a2
b. zero
c. e2/16mπε0a2
d. none of the above

8.The potential energy of a certain particle is given by
U=20x2+35z3.Find the vector force on it
a. -40xi-105z2k
b. 40xi-105z2k
c.-10xi-105z2k
d 40xi+105z2k

Matrix Match type

9.
Column I
a. Frictional force
b. Gravitational force
c. Electrical force
d Viscous force

Column II
P. Workdone by the force in closed loop is zero
Q. Workdone by the force in closed loop is not zero 
 
 
 
 
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Multiple choice question with one answer

1.A IITJEE text book of mass M rests flat on a horizontal table of mass m placed on the ground.Let RX->Y be the constant force exerted by the body x on body Y.According to Newton third law,which of the following is an action-reaction pair of forces?

a. (M+m)g and Rtable->book
b. Rground->table and mg+Rbook->table
c. Rground->table and Rtable->ground
d Mg and Rtable->book


2. there are two statements
A Newtons first law in valid from the pilot in an aircraft which is taking off
B Newtons first law in valid from the observer in a train moving with constant velocity
Which of the following is correct

(a) A only
(b) B only
(c) Both A and B are correct
(d) Both A and B are wrong


3.The horizontal and vertical displacement of the projectile at time t are
x=36t
y=48t-4.9t2
where x and y are in meters and t in second.Intial velocity of the projectile in m/s
a. 15
c. 30
b. 45
d. 60


4.A truck accelerates from rest at the constant rate a for some time after which it decelerates at a constant rate of b to come to the rest.If the total time elapsed is t ,then find out the maximum velocity attains by the truck
a. (ab/a+b)t
b.(a+b/ab)t
c. (a2+b2/ab)t
d.(a2-b2/ab)t


5.A boy playing on the roof of a 10 m high building throws a ball with a speed of 10 m/s at an angle of 30 ° with the horizontal. How far from the throwing point will the ball be at the height of 10 m from the ground? take g = 10 m/s2
a. 5.20 m
b.4.33 m
c.2.60 m
d 8.66 m.

Multiple choice question with one or more answer

1. A body is projected horizontally from a point above the ground.The motion of body is defined as
x=2t
y=2t2
where x and y are horizontal and vertical displacement respectivley at time t.Which one of the following is true
a.The trajectory of the body is a parabola
b The trajectory of the body is a straight line
c.the velocity vector at point t is 2i+4tj
d the acceleration vector at time t is 4j


2.Mark out the correct statement
a)Instantaneous Velocity vector is always in the direction of the motion
b)Instantaneous acceleration vector is always in the direction of the motion
c)Acceleration of the moving particle can change its direction with any change in direction of velocity
d) None of the above




Assertion and Reason
a) Statement I is true ,statement II is true ,statement II is correct explanation for statement I
b) Statement I is true ,statement II is true ,statement II is not a correct explanation for statement I
c) Statement I is true,Statement II is false
d) Statement I is False,Statement II is True

1. STATEMENT1: The Average velocity of a continously moving particle may be zero for some time interval but average speed will not be zero
STATEMENT: Displacement of a continously moving particle can decrease with time but distance will not


2. STATEMENT1: Two bodies of mass m and M will reach ground in same time when fallen at same time from the tower of height h
STATEMENT1: Same Acceleration due to gravity is experienced by the both body in fall from tower


3.STATEMENT1:In a projectile motion,acceleration vector is Perpendicular to Velocity vector at the highest point
STATEMENT:There is no horizontal acceleration present in the projectile motion




Matrix match type
In a free fall motion from rest,Match column I to column II
column I
A) Graph between displacement and time
B) Graph between velocity and time
C) Graph between velocity and displacement
D) Graph between KE and displacement

column II
P) Parabola
Q) Straight line
C) Circle
D) No appropiate match given

Linked Comphrehension type
.A train is moving in the west direction with a velocity 15m/s.A monkey runs on the roof of the train against its motion with a velocity 5m/s with respect to train .Take the motion along west as positive
1.Velocity of train relative to its driver
a. 0
b. 15 m/s
c. -15 m/s
d. 20 m/s

2. What is the velocty of train with respect to monkey
a. 5m/s
b -5 m/s
c. 15 m/s
d -15 m/s

3. find the velocty of ground with respect to monkey
a. 5 m/s
b. -5 m/s
c. 10 m/s
d. -10 m/s 

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