Physics Test 242

Result

Physics Test 242

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Question 1
4 / -1

A
96 N

B
108 N

C
120 N

D
150 N

Solution
Question 2
4 / -1

5 mol of liquid water is compressed from 1 bar to 10 bar at constant temperature. Change in Gibb's energy ΔG in Joule is : [Density of water = 1000 kg/m³].

A
18

B
225

C
450

D
900

Solution
Question 3
4 / -1

The difference between the apparent frequency of a source of sound as perceived by an observer during its approach and recession is 2% of the natural frequency of the source. If the velocity of sound in air is 300 m/sec, the velocity of the source is (It is given that velocity of source << velocity of sound)

A
6 m/sec

B
3 m/sec

C
1.5 m/sec

D
12 m/sec

Solution
Question 4
4 / -1

A body slides down a frictionless track which ends in a circular loop of diameter D. Then the minimum height h of the body in terms of D so that it may just complete the loop, is

A

B

C

D

Solution
Question 5
4 / -1

The effective resistance of a parallel connection that consists of four wires of equal length, equal area of cross-section and same material is 0.25 Ω. What will be the effective resistance if they are connected in series ?

A
4 Ω

B
0.25 Ω

C
0.5 Ω

D
1 Ω

Solution

All the wires are identical and of same material so they will have same value of resistance. Let it be R. When these are (four) connected in parallel.
Question 6
4 / -1

A set of 'n' equal resistors, of value 'R' each, are connected in series to a battery of emf 'E' and internal resistance 'R'. The current drawn is I, Now, the 'n' resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10 I. The value of 'n' is

A
10

B
11

C
9

D
20

Solution

CONCEPT:

As we know that the relation between the EMF 'E' and internal resistance 'R' is written as;

E = I(r+R) ----(1)

Here E is the 'EMF', r is the internal resistance and R is the load resistance.

Resistance in series- When n numbers of resistors are in series then the total resistance is written as;

Now, the n number of resistance are connected parallel and the current drawn is 10I we have;
Question 7
4 / -1

Two point charges A and B, having charges +Q and −Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes :

A
F

B

C

D

Solution

CONCEPT:

Coulomb's law - According to this law, states that the force of attraction and repulsion between two bodies is directly proportional to the product of the charges of two-body and inversely proportional to the square of the distance between them. It is written as;

Here,q_A and q_B are the charges of body A and body B, r is the distance between the body and K is the constant of proportional which is the equation.

CALCULATION:

Given that two-point charges A and B, having charges +Q and −Q and placed at the distance r is shown in the figure below,
Question 8
4 / -1

When a block of mass M is suspended by a long wire of length L, the length of the wire becomes (L + l). The elastic potential energy stored in the extended wire is :

A
Mgl

B
MgL

C

D
Solution
Concept:

Stress- It is defined as the force acting per unit area.

Stress = Force/Area

Strain- It is defined as deformation produced in a body in the direction of application of force divided by original dimensions of the body.

Strain = Change in length/Original length

Strain = ΔL/L

where L is the original length and ΔL is the change in the length of the wire.

Elastic potential energy-
- It is a type of potential energy stored by the deformation of an elastic material. For example- Energy stored in a spring when it is either compressed or stretched.
- Elastic potential energy = force × displacement
According to Hooke’s law, the force applied to stretch the spring is directly proportional to the amount of stretch. In terms of displacement, the force required to stretch the spring is directly proportional to its displacement.

F ∝ - x

where F is the force applied on the spring and x is the displacement or amount of stretch.

The negative sign indicates displacement is in the opposite direction of the force.

hence, F = -kx, where k is spring constant.

The elastic potential energy of stretched spring is ,
Question 9
4 / -1

A convex lens ‘A’ of focal length 20 cm and a concave lens ‘B’ of focal length 5 cm are kept along the same axis with a distance ‘d’ between them. If a parallel beam of light falling on ‘A’ leaves ‘B’ as a parallel beam, then the distance ‘d’ in cm will be(minimum) :

A
30

B
25

C
15

D
50

Solution

CONCEPT:

A parallel beam of light after refraction from a convex lens converges at the focus of the convex lens. In question, it is given that light after refraction pass through a concave lens and becomes parallel. Therefore light refracted from the convex lens virtually meets the focus of the concave lens.

CALCULATION:

Given: Focal length, f_A = 20 cm

and focal length, f_B = 5 cm

d is the distance.

If a parallel beam of light falling on ‘A’ leaves ‘B’ as a parallel beam is shown in the figure below.

According to the above ray diagram, we can see that distance d is equal to,

d = f_A – f_B

⇒ d= 20 – 5

⇒ d = 15 cm
Question 10
4 / -1

A particle of mass 200 g is thrown vertically upwards with a speed of 10 m/s. The work done by the force of gravity during the time the particle goes up is:

A
-5 J

B
5 J

C
-10 J

D
10 J

Solution

Concept: