Physics Test 216

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Physics Test 216

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Question 1
4 / -1

The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?

A
L,C

B
L alone

C
C alone

D
R alone

Solution

If the phase difference between V and I is π/2

∴ Power = V .I = V I cosπ/2 = 0

Since power is 0 it should only consists of reactive elements (L & C), Resistance R cannot be present.
Question 2
4 / -1

If a wire is stretched to make it 0.1% longer, its resistance will

A
increase by 0.05%

B
increase by 0.2%

C
decrease by 0.2%

D
decrease by 0.05%

Solution

Hence, when the wire is stretched by 0.1%, its resistance will increase by 0.2%.
Question 3
4 / -1

Directions For Questions

Directions: The following question contains statement-1 and statement-2. Of the four choices given, choose the one that best describes the two statements.

...view full instructions

Statement-1: For a mass M kept at the centre of a cube of side a, the flux of gravitational field passing through its sides is 4πGM.

Statement-2: If the direction of a field due to a point source is radial and its dependence on the distance r from the source is given as 1/r², its flux through a closed surface depends only on the strength of the source enclosed by the surface and not on the size or shape of the surface

A
Statement-1 is true, statement-2 is false.

B
Statement-1 is false, statement-2 is true.

C
Statement-1 is true, statement-2 is true; statement-2 is a correct explanation for statement-1.

D
Statement-1 is true, statement-2 is true; statement-2 is not a correct explanation for statement-1.

Solution

Every line passing through A has to pass through B, whether B is a cube or any surface. It is only for Gaussian surface that the lines of field should be normal, assuming the mass to be a point mass.

Here, B is a cube. As explained earlier, whatever be the shape, all the lines passing through A are passing through B, although all the lines are not normal.

Statement-2 is correct because when the shape of the earth is spherical, area of this Gaussian surface is 4πr². This ensures inverse square law.
Question 4
4 / -1

When the current in the portion of the circuit, shown in the figure, is 2 A and is increasing at the rate of 1 A/s, then the measured potential difference V_ab is 8 V. However, when the current is 2 A and is decreasing at the rate of 1 A/s, the measured potential difference V_ab is 4V. The values of R and L are

A
3 Ω and 2 H, respectively

B
2 Ω and 3 H, respectively

C
10 Ω and 6 H, respectively

D
6 Ω and 1 H, respectively

Solution

For the first case, when the current is increasing di/dt = 1A / s

8 = 2R + L …..(1)

For the first case, when the current is increasing di/dt = -1A / s

4 = 2R - L …..(2)

From 1 and 2, R = 3Ω, L = 2H
Question 5
4 / -1

Identify the wrong statement.

A
Friction always opposes motion.

B
Friction always opposes relative motion between two surfaces.

C
Friction acts between two rough surfaces in contact with each other.

D
Friction always acts opposite to the direction of motion or intended motion.

Solution

Friction always opposes motion is the incorrect statement as the friction can produce the motion in the object.

Consider the following figure:

When the force is applied on the lower block, friction will come into action between the surface and lower block and, between the lower block and upper block. The friction between upper and lower block will cause the upper block to move with the lower block.
Question 6
4 / -1

A particle of mass m is at rest at the origin at time t = 0. It is subjected to a force F(t) = F₀e^-bt in the x direction.

Which of the following curves depicts its speed v(t)?

A

B

C

D

Solution
Question 7
4 / -1

A wire elongates by l mm when a load W is hanged from it. If the wire goes over a pulley and two weights W each are hung at the two ends, the elongation of the wire will be (in mm)

A
l/2

B
l

C
2l

D
zero

Solution

For the wire having length L, the elongation in the wire is given by l.

Hence, total increase in length on both sides is l.
Question 8
4 / -1

Two particles, A and B, of equal masses are suspended from two massless springs of spring constants k₁ and k₂, respectively. If the maximum velocities, during oscillations, are equal, then the ratio of amplitudes of A and B is

A

B
k₂/k₂

C

D
k₁/k₂

Solution
Question 9
4 / -1

At some instant, a particle is moving along a straight line 2x - 3y = 2 and its co-ordinates on that line are (4, 2). Now, at another instant, the same particle is moving along a straight line 3x + 4y = 7 and its co-ordinates are (1, 1). Find the co-ordinates of that axis about which it is in pure rotation.

A
30/17 , 35/17

B
50/17 , 61/17

C
8/9 , 16/9

D
None of these

Solution

Axis of pure rotation will be on the perpendicular line of both the straight lines.

Intersection of these two lines passing through (4, 2) and (1, 1) will be the co-ordinates of the axis of pure rotation.

The line given by 2y + 3x = 16 is perpendicular to 2x - 3y = 2 and the line given by 3y - 4x = -1 is perpendicular to 3x + 4y = 7.

On solving 2y + 3x = 16 and 3y - 4x = -1, we get

x = 50/17 and y = 61/17
Question 10
4 / -1

The amplitude of wave disturbance propagating in the positive x-axis is given by at t = 2s, where x and y are in metres. The shape of the disturbance does not change during the propagation. The velocity of the wave is

A
1 m/s

B
0.5 m/s

C
2 m/s

D
1.5 m/s

Solution