IIT JAM Physics MCQ Test 1

30 Questions MCQ Test Mock Test Series for IIT JAM Physics | IIT JAM Physics MCQ Test 1

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A body of mass m is suspended by two strings makings angle α and β with the horizontal. Find the tension T1 in the strings.


Force acting on the system are shown in Fig.
For equilibrium in horizontal direction.
T1 cos∝ = T2 cosβ .....(1)
For equilibrium in vertical direction,
T1 sin∝ = T2 sinβ - mg = 0 .....(2)
From(1)  ....(3)
Put in (2)

T1(sinα cosβ+cosαsinβ) =  mgcosβ
T1sin (α+β) = mg cosβ

Put in (3)


A body of mass 5 kg is acted upon by  two perpendicular forces 8 N and 6 N. The magnitude and possible direction of the acceleration of the body are 


Here, m = 5kg,

Resultant force, 

θ = 36052'
This is the direction  of resultant force and hence the direction of acceleration of the body. Fig.



The relation between time t and distance x is t = ax+ bx where a and b` are constants. The acceleration is



A particle moves from rest at P1 on the surface of a smooth circular cylinder of radius R as shown in Fig. At P2 the particle leaves the cylinder. The relation between θ1 and θ2 is: 


As the normal force does no work on the particle, its energy is conserved.
So (L.E. + P.E.)P1= (K.E. + P.E.)P2
(K + U)P1 = (K + U)P2......(1)
Initially the particle in rest at P1 so kinetic energy (V = 0) will be zero at P1.
So from equation(1)

mgR cosθ1 is potential energy at 
P1 = mgh
h → height = Rcosθ1

At point P2 potential energy is mgh = mg Rsinθ2

 [using 2]



The velocity of pendulum bob, which has been pulled aside from  its equilibrium position through an angle θ and then released and it will pass through the equilibrium position, (where L is the length of the pendulum):


Using the conservation of energy law in the form
Loss of PE = gain of KE

From Fig.
h = I - I cosθ


A rocket motor consumes one quintal of fuel per second. The exhaust speed of gasses w.r.t. rocket is 5 km/s. The force exerted on the rocket and velocity acquired by the rocket, when its mass reduces to 1/100th of its initial mass is:


u = -5km/s = -5 x 103m/s

F = -(-5 x 103) (100) = 5 x 105N

= 5 x 103loge100 = (5 x103)
= 5 x 103 x 2.303 x 2
= 2.303 x 104 m/s.


A bullet is fired horizontally in the north direction with a velocity of 500m/sec. at 300N latitude. The horizontal component of Coriolis acceleration is: 


If X- axis is taken vertically, Z-axis towards north and Y-axis along east, then the velocity of the bulled is v = 500km/sec. and angular velocity w = w  because the angular velocity vector w of the earth is directed parallel to its axis and is inclined at 300 to the horizontal

Hence Coriolis acceleration
= 2w x v

 m/sec2 towards west.


A canon launches a metal ball horizontal using a spring as the firing mechanism. The canon has mass mcanon and the mball. The spring constant is k. Initially, the spring is compressed a distance d  from its equilibrium length. What is ncannon/nball, the ratio of the cannon's recoil velocity to the ball's velocity? 


By conservation of momentum, Pcannon = -Pball'


A satellite is in elliptical orbit about the earth (radius = 6400km). At perigee it has an altitude of 1100 km and at the apogee its altitude is 4100km.The major axis of the orbit is at the distance.


By the property of ellipse 
Major axis 2a = maximum distance + minimum distance

Maximum distance =  maximum altitude + radius of earth = (4100+6400)
Minimum distance from centre of earth = 6400 + 1100
So, 2a = (4100+6400)+(6400+1100) = 18000km


A particle describes a circular orbit under the influence of an attractive central force directed towards a point on the circle,then the force is inversely proportional to,


For attractive central force,

So,  ...(1)
Now substitute equation(2) in euqation of orbit

and from equation(1), seq q= 2au



If f α -rn, then for what value of n, the circular orbit described is stable?


f(r) a -rn
f = -krn
Where k is a constant

= arn+1   where (new constant)
Condition for stable orbit

If the potential energy  function for the central force is of the form  and centrifugal energy 

The condition for the stability in the radial motion is

So, differentiate equation (1) w.r.to r 

Thus any circular orbit with r = runder a central force is stable


For a rigid body, linear velocity  and angular velocity 'w' are related as;





The linear mass density l of a rod, of uniform area of cross-section, 1 m long, varies with the distance x from its left end as given by 

The centre of mass of the rod is located, from the left end, at a distance of:


The centre of mass    Q(dm = λdx)


Figure shows a system of three initially resting particles of masses m1 = 4.1kg, m= 8.2kg./ and m3 = 4.1kg.The particles are each acted on by different net external forces, which have magnitudes F1 = 6N, F2 = 12N and F3 = 14N. The directions of the forces are shown in the figure. Where is the center of mass of this system?


The position of the center of mass is marked by a dot in the figure. As figure suggests, we treat this point as if it held a real particle, assigning to it a mass M equal to the system mass of m1 + m2 m3 = 16.4kg and assuming that all external forces are applied at that point. We find the center of mass from equation

The x component of the net external force acting on the center of mass is


Find the centre of mass of a uniform disc of radius a from whhich a circular section of radius b has been removed. The centre of hole is at a distance c from the centre of the disc.


Suppose the circular disc of radius a with centre O is made up of 
(i) Circular section of radius b with centre O1 and
(ii) Remaining portion  of disc with cm at O2
Taking O as origin, and O1, O2 on X-axis, (y = 0, z = 0), figure the position of cm of disc is given by
If s is surface density of material of the disc.

*Multiple options can be correct

A particle is moving in space with O as the origin. Some possible expressions for its position velocity and acceleration in cylindrical coordinate (p,φ,z) are given below, which of the following are correct?


In this coordinate system, we have the three coordinates as 

These coordinate are related to the cartesian coordinates by the relations

Position vector r is given by

Hence, the velocity is given by 
Differentiating above equation with respect to time, we get acceleration

*Multiple options can be correct

For a particle moving in a central potential, which one of the following statements is correct? 


Two types of central force always produce closed orbits: F(r) = αr (a linear force) and F(r) = α / r2 (an inverse-square law).

*Multiple options can be correct

A ball of mass m is thrown upward with velocity v and return back with v'. If air exerts an average resisting force F. Then


Retarding force = mg +F.
Retardation a = 
Distance s = 
Downward motion: Force = mg -F
Acceleration a' = 
Distance's =  
Sinces =  S, we have 

*Multiple options can be correct

A bullet of mass 10gm is fired horizontally in the north direction with a velocity of 500m/sec at 300N latitude and it hits a target 250 meters away. Then


If X-axis is taken vertically, Z-axis towards north and Y-axis along east, then the velocity of the bullet is v = 500 km/sec. and angular velocity - UTP2  because the angular velocity vector ww of the earth is directed parallel to its axis and is inclined at 300 to the horizibtal.

Hence coriolis acceleration

Time of journey, t 
Deflection of the bullet due to the coriolis acceleration

Vertical displacement of the bulet due to the gravity

Coriolis force = -2m w x v

=3.6 x 10-4 newton towwards east.

*Multiple options can be correct

A body of mass 2 kg moves under the influence of a central force, with a potential energy function  Joule, where r is the radius circular orbit and r = 5m  
The corresponding angular momentum  and total energy are L and E. Then


The body moves in a circular orbit of radius r = 5ms
So, energy of the system will always be equal to ve at r = 5m
Also, ve will be maximum at r = 5m and dve/dr will be zero at r = 5m

The body moves in a circular orbit of radius r = 5m
So, energy of the system will always be equal to ve at r = 5m
Also, ve will be maximum at r = 5m and dve/dr will be zero at r = 5m

*Answer can only contain numeric values

A man travelling in a car with a maximum constant speed of 20m/s watches his friend start off at a distance of 100m on a motor cycle with constant accelerationa. Then man in the car will reach his friend when a is .......m/sec2.


0 to 2

Let the man was initially at A and moves towards B with uniform velocity u = 20m/s.
Let the man in car meets the man B at point Q, then
AQ= 100 + BQ

The value of t will be real, if 

*Answer can only contain numeric values

A thin uniform rod XY of mass 0.1 kg and length 0.3m is hinged at its lowe end at X to the horizontal floor. It originally stands vertical and is allowed to fall to the floor. It strikes the floor with an angular speed of (rad/sec).......


By the law of conservation of energy 

Total energy at A = total energy at B

*Answer can only contain numeric values

A bullet of mass 0.01kg and travelling at a speed of 500m/s strikes a block of mass 2 kg which is suspended by a string of length 5m. The centre of gravity  of the block is found to rise a vertical distance of 0.1m. What is the speed(m/s) of the bullet after it emerges from the block? (g=9.8m/s2).


Let V be the velocity acquire by the block.

If n' is speed of bullet on emerging out of block, then by law of conservation of momentum, we get 
mn +M x 0 = MV +Mn'

*Answer can only contain numeric values

A toy rocket of mass 0.1 kg has a small fuel of mass 0.02kg which it burns out in 3s. Starting from rest on a horizontal smooth track, it gets a speed of 20 ms-1 after the fuel is burnt out. What is the approximate thrust of the rocket? What is the energy (joules/kg) content per unit mass of the fuel? (Ignore the small mass variation of the rocket during fuel burning)


Herem mass of rocket, 
m1 = 0.1 kg,
mass of fuel, m2 = 0.02 kg, t = 3s
Initial velocity u = 0
final velocity n = 20m/s
from n = u+at

Thrust on the rocket, 
If s is the distance moved by the rocket in 3 sec, then from

Energy content of the fuel = work done on 
rocket = Thrust x distance = 

Energy/kg = 20/0.02 = 1000 J/kg

*Answer can only contain numeric values

A wooden block having a mass of 1 kg is placed on a table. The block just starts to move, when a force of 10N is applied at 450 to the vertical to push the block. The coefficient of friction between the table and the block, (taking g = 10m/s2) is approximately________


Resolving the forces and finding their horizontal and vertical component
mg = R + Fcosθ
Frictional force = F sinθ
By Eq.(ii) we get

= 0.8

*Answer can only contain numeric values

A particle moves in a plane with velocity  such that  the time dependence of the magnitude of the velocity is  It is given that at  At what time (sec) will θ become 4 radian?


*Answer can only contain numeric values

A boy stands at 78.4m from a building and throws a ball which just enters a window 39.2m above the ground Calculate the velocity of projection (ms-1) of the ball



Let a boy standing at A throw a ball with a velocity u at an angle q with the horizontal, which just enters window W.
As the boy is at 78.4 m from the building and the ball just enters the window 39.2m above the ground, therefore

And horizontal range,

Dividing (i) by (ii), we get

Substituting in (ii), we get

*Answer can only contain numeric values

A satellite of mass 100 kg is placed initially in a temporary orbit 800km above the surface of earth. The satellite is to be placed now in a permanent orbit at 2000km above the surface of earth. Find the amount of work done (mega joule) to move the satellite from temporary to permaanent orbit. The radius of the earth is 6400km. Given g = 10m/s2.


Consider a satellite of mass m is orbiting around the earth with orbit velocity n. Let h be the height of satellite from the surface of earth and r be the orbital radius of the satellite. Then

Total energy the orbiting satellite (E)

Work done in shifting the satellite from height h to h1 is 
W = difference in energy of satellite in two orbits 

*Answer can only contain numeric values

A rocket of initial 6000kg ejects mass at a constant rate of 16kg/s with constant relative speed of 11km/s. What is the acceleration (in m/s2) of the rocket on minute after blast?


= 34.92m/s2

*Answer can only contain numeric values

A soccer ball has a mass of 0.40kg. Initially, it is moving to the left at 20m/s but then it is kicked and given a velocity at 450 upward  and to the right with a magnitude of 30m/s figure. Find the average net force (inN), asuming a collision time dt= 0.010s.


With our choice of axes, we find the following velocity components:

The x- component of impulse is equal to the x-component of momentum change, and the same is true for they y-components.

The components of the average net force on the ball are 

The magnitude and directionn of the average force are 

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