JEE MAIN - Physics (2021 - 31st August Morning Shift)
1
A helicopter is flying horizontally with a speed 'v' at an altitude 'h' has to drop a food packet for a man on the ground. What is the distance of helicopter from the man when the food packet is dropped?
Answer
(C)
$$\sqrt {{{2{v^2}h} \over g} + {h^2}} $$
2
In the following logic circuit the sequence of the inputs A, B are (0, 0), (0, 1), (1, 0) and (1, 1). The output Y for this sequence will be :
Answer
(C)
1, 1, 1, 0
3
Two particles A and B having charges 20$$\mu$$C and $$-$$5$$\mu$$C respectively are held fixed with a separation of 5 cm. At what position a third charged particle should be placed so that it does not experience a net electric force?
Answer
(B)
At 5 cm from $$-$$5 $$\mu$$C on the right side
4
An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens?
Answer
(C)
$${1 \over 2}$$, $${f \over 2}$$
5
A coil having N turns is wound tightly in the form of a spiral with inner and outer radii 'a' and 'b' respectively. Find the magnetic field at centre, when a current I passes through coil:
A body of mass M moving at speed V0 collides elastically with a mass 'm' at rest. After the collision, the two masses move at angles $$\theta$$1 and $$\theta$$2 with respect to the initial direction of motion of the body of mass M. The largest possible value of the ratio M/m, for which the angles $$\theta$$1 and $$\theta$$2 will be equal, is :
Answer
(C)
3
7
The masses and radii of the earth and moon are (M1, R1) and (M2, R2) respectively. Their centres are at a distance 'r' apart. Find the minimum escape velocity for a particle of mass 'm' to be projected from the middle of these two masses :
Answer
(B)
$$V = \sqrt {{{4G({M_1} + {M_2})} \over r}} $$
8
A small square loop of side 'a' and one turn is placed inside a larger square loop of side b and one turn (b >> a). The two loops are coplanar with their centres coinciding. If a current I is passed in the square loop of side 'b', then the coefficient of mutual inductance between the two loops is :
Choose the correct waveform that can represent the voltage across R of the following circuit, assuming the diode is ideal one :
Answer
(D)
10
A uniform heavy rod of weight 10 kg ms$$-$$2, cross-sectional area 100 cm2 and length 20 cm is hanging from a fixed support. Young modulus of the material of the rod is 2 $$\times$$ 1011 Nm$$-$$2. Neglecting the lateral contraction, find the elongation of rod due to its own weight.
Answer
(D)
5 $$\times$$ 10$$-$$10 m
11
Two plane mirrors M1 and M2 are at right angle to each other shown. A point source 'P' is placed at 'a' and '2a' meter away from M1 and M2 respectively. The shortest distance between the images thus formed is : (Take $$\sqrt 5 $$ = 2.3)
Answer
(B)
4.6a
12
Match List - I with List - II.
List - I
List - II
(a)
Torque
(i)
MLT$$^{ - 1}$$
(b)
Impulse
(ii)
MT$$^{ - 2}$$
(c)
Tension
(iii)
ML$$^{ 2}$$T$$^{ - 2}$$
(d)
Surface Tension
(iv)
MLT$$^{ - 2}$$
Choose the most appropriate answer from the option given below :
Answer
(A)
(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
13
For an ideal gas the instantaneous change in pressure 'p' with volume 'v' is given by the equation $${{dp} \over {dv}} = - ap$$. If p = p0 at v =0 is the given boundary condition, then the maximum temperature one mole of gas can attain is : (Here R is the gas constant)
Answer
(A)
$${{{p_0}} \over {aeR}}$$
14
Which of the following equations is dimensionally incorrect?
Where t = time, h = height, s = surface tension, $$\theta$$ = angle, $$\rho$$ = density, a, r = radius, g = acceleration due to gravity, v = volume, p = pressure, W = work done, T = torque, $$\in$$ = permittivity, E = electric field, J = current density, L = length.
Answer
(A)
$$v = {{\pi p{a^4}} \over {8\eta L}}$$
15
Angular momentum of a single particle moving with constant speed along circular path :
Answer
(B)
remains same in magnitude and direction
16
In an ac circuit, an inductor, a capacitor and a resistor are connected in series with XL = R = XC. Impedance of this circuit is :
Answer
(C)
R
17
A moving proton and electron have the same de-Broglie wavelength. If K and P denote the K.E. and momentum respectively. Then choose the correct option :
Answer
(A)
Kp < Ke and Pp = Pe
18
Consider a galvanometer shunted with 5$$\Omega$$ resistance and 2% of current passes through it. What is the resistance of the given galvanometer ?
Answer
(C)
245 $$\Omega$$
19
When a rubber ball is taken to a depth of __________m in deep sea, its volume decreases by 0.5%.
(The bulk modulus of rubber = 9.8 $$\times$$ 108 Nm$$-$$2, Density of sea water = 103 kgm$$-$$3, g = 9.8 m/s2)
Answer
500
20
A particle of mass 1 kg is hanging from a spring of force constant 100 Nm$$-$$1. The mass is pulled slightly downward and released so that it executes free simple harmonic motion with time period T. The time when the kinetic energy and potential energy of the system will become equal, is $${T \over x}$$. The value of x is _____________.
Answer
8
21
A square shaped wire with resistance of each side 3$$\Omega$$ is bent to form a complete circle. The resistance between two diametrically opposite points of the circle in unit of $$\Omega$$ will be ___________.
Answer
3
22
A wire having a linear mass density 9.0 $$\times$$ 10$$-$$4 kg/m is stretched between two rigid supports with a tension of 900 N. The wire resonates at a frequency of 500 Hz. The next higher frequency at which the same wire resonates is 550 Hz. The length of the wire is ____________ m.
Answer
10
23
The voltage drop across 15$$\Omega$$ resistance in the given figure will be ______________ V.
Answer
6
24
A block moving horizontally on a smooth surface with a speed of 40 ms$$-$$1 splits into two equal parts. If one of the parts moves at 60 ms$$-$$1 in the same direction, then the fractional change in the kinetic energy will be x : 4 where x = ___________.
Answer
1
25
The electric field in an electromagnetic wave is given by E = (50 NC$$-$$1) sin$$\omega$$ (t $$-$$ x/c)
The energy contained in a cylinder of volume V is 5.5 $$\times$$ 10$$-$$12 J. The value of V is _____________ cm3. (given $$\in$$0 = 8.8 $$\times$$ 10$$-$$12C2N$$-$$1m$$-$$2)
Answer
500
26
A capacitor of 50 $$\mu$$F is connected in a circuit as shown in figure. The charge on the upper plate of the capacitor is ______________$$\mu$$C.
Answer
100
27
A car is moving on a plane inclined at 30$$^\circ$$ to the horizontal with an acceleration of 10 ms$$-$$2 parallel to the plane upward. A bob is suspended by a string from the roof of the car. The angle in degrees which the string makes with the vertical is ______________. (Take g = 10 ms$$-$$2)