Physics Practice Test 2

Q.1

Force acting on an object is given as F = Xx-1
(Where x is the distance by which the body is displaced due to the applied force)
What would be the dimensional formula for X?

• A. MLT-2
• B. MLT-1
• C. M-1LT-1
• D. M-1L2T-1
• E. ML2T-2
• Explanation: From dimensional analysis we know that dimensional formula of the left hand side of an expression should be the same be the same as the dimensional formula of the individual quantities on the right hand side. Force has the SL unit of. Therefore, the dimensional formula of force becomes. Dimensional formula of is L. Hence, dimensional formula of becomes. As said earlier, should have the same dimensional formula as F. Therefore, it can be written as
MLT-2 = X * L-1
X = ML2T-2
Therefore, E is the correct answer option.

Q.2

Consider the figure and the statements given below. ( v is velocity and t is time)
1. The graph is for a body that is accelerating
2. The graph is for a body that is falling freely
3. The graph is for a body that has constant velocity
Which of the following statement(s) is true in accordance to the given figure? • A. 2
• B. 1
• C. 3
• D. Both 1 and 2
• E. Both 2 and 3
• Explanation: The graph given in the question is between velocity and time. Slope of the velocity time graph is linear here. Therefore, velocity increase with each instant but change in velocity per unit time is constant throughout the travel. Thus, 3 is an incorrect statement and so is option C. Acceleration of a body is defined as the rate of change of velocity per unit time. As said earlier, for a linear slope between velocity and time, change in velocity is constant per unit time and thus, acceleration is constant for the entire travel. Therefore, statement 1 is incorrect and so is option B. A body falls freely under gravity only. A free failing body always experiences uniform acceleration throughout the travel. Thus, we can say that acceleration is constant for a free fall and the graph essentially represents the motion of free fall. Thus, statement 2 is correct and so A is the correct answer option. In view of the above discussion, options D and E are incorrect as well.

Q.3

If a block of wood weighs 1000 N, What would be its mass?

• A. 102.04 kg
• B. 10.24 kg
• C. 1020.44 kg
• D. 1.24 kg
• E. 110.24 kg
• Explanation: Weight of a body is given as
W = mg ------------(1)
Putting the value of W and g in equation 1 we get
1000 = m * 9.8
m = 102.04 kg
Therefore, A is the correct answer option.

Q.4

A force of 25 N is acting along the North direction and a force of 12 N is acting along the South direction on a body of mass 1.5 kg. What acceleration will the force bring in the body?

• A. 9.87 m/s2
• B. 2.36 m/s2
• C. 4.67 m/s2
• D. 7.67 m/s2
• E. 8.67 m/s2
• Explanation: A body undergoes acceleration due to an unbalanced force. The unbalanced force here is given as
F = 25 ??? 12 Or F = 13 N
According to Newton???s second law of motion
F = ma ---------------(1)
13 = 1.5 * a
a = 8.67 m/s2
Therefore, E is the correct answer option.

Q.5

If a wheel is rotating with an angular velocity of 2.5 rad/s, what is the time taken by the wheel to complete one full rotation?

• A. 1.57 s
• B. 2.51 s
• C. 1.84 s
• D. 3.52 s
• E. 2.22 s
• Explanation: Time taken to complete one rotation is known as time period. Angular velocity is related to time period as
?? = 2?? / T -------------(1)
Putting the values of (?? = 3.14) and ?? in equation 1 we get
2.5 = (2 * 3.14) / T
T = 2.51 s
Therefore, B is the correct answer option.

Q.6

An object is to be lifted from the ground to a height of 5m in 25 seconds. If the energy consumed during the process is 2000 J, what is the power required?

• A. 75 J/s
• B. 72 J/s
• C. 80 J/s
• D. 100 J/s
• E. 125 J/s
• Explanation: Power is given as
P = W / t ------------(1)
Putting the values in equation 1 we get
P = 2000 / 25
P = 80 J / s or watt
Hence, C is the correct answer option.

Q.7

A block of mass M, connected to a spring of spring constant k ( a spring-mass system ), is executing SHM with time period, T on Earth. If the same system executes SHM on the surface of Moon, what will be the new time period?

• A. More than that on the Earth
• B. Less than that on the Earth
• C. Same as that on the Earth
• D. Zero
• E. Not enough data is provided to predict the answer
• Explanation: Time period is given as
T = 2 ?? ???(M/k) --------------(1)
At the surface of the Moon, acceleration due to gravity is (1/6)th of that on the surface of the Earth. As, there is no term related to acceleration due to gravity in equation 1, time period of the system will remain unaffected. Hence, time period of the system on the moon will be the same as that of the system on the Earth. Therefore, C is the correct answer option.

Q.8

If the speeds of sound in solid, liquid and gas are arranged in increasing order, which of the following is a correct arrangement?

• A. Solids < liquids < gas
• B. Liquids < solids < gas
• C. Gas < liquids < solids
• D. Gas < solids < liquids
• E. Liquids < gas < solids
• Explanation: The speed of sound in solids like steel and iron is 5000 m/s and 5130 m/s. The speed of sound in liquids like water at 00C and 200C is 1402 m/s and 1482 m/s respectively. The speed of sound in air (gas) at 00C and 200C is 331.5 m/s and 344 m/s respectively. Thus, from the above discussion it can be concluded that the speed of sound in solids is more than that in liquids and air. Therefore, the correct arrangement for speeds of sound air (gas) < liquids < solids. Thus, C is the correct answer option.

Q.9

What would be the specific gravity of a fluid having density of 944 kg / m3?

• A. 0.967
• B. 0.456
• C. 0.944
• D. 0.789
• E. 0.45
• Explanation: Specific gravity is a dimensionless quantity and is given as
SG = ??fluid / ??water ------------(1)
It is quite obvious from equation 1 that specific gravity is a unit less quantity. Putting the values of densities in equation 1 we get
SG = 944/1000
Or SG = 0.944
Therefore, C is the correct answer option.

Q.10

A sample of gas at 313 K occupies a volume of 10 m3. What would be its volume at 373 K?

• A. 11.92 m3
• B. 15.56 m3
• C. 10.45 m3
• D. 12.67 m3
• E. Cannot be determined
• Explanation: This equation can be solved by applying Charles???s law, which is given as
(V1 / T1) = (V2 / T2) -------------(1)
Putting the values in equation 1 we get
(10 / 313) = (V2 / 373)
V2 = 11.92 m3
Therefore, A is the correct answer option.

Q.11

What is the dipole moment between an electron and a proton separated by a distance of 1 nm?

• A. 3.6 * 10-28 Cm
• B. 4.5 * 10-28 Cm
• C. 4.5 * 10-26 Cm
• D. 1.6 * 10-28 Cm
• E. 3.2 * 10-28 Cm
• Explanation: Electric dipole moment between two charges of opposite polarity is given as
p = Qd ----------(1)
The distance is in nm so we need to convert it into m.
1 nm = 10-9 m
Putting the values in equation 1 we get
P = 1.6 * 10-19 * 10-9
Or, 1.6 * 10-28 Cm
Hence, D is the correct answer option.

Q.12

For a conductor having a cross section of 2*10-4 m2, average drift velocity of the electrons flowing through it is 10-3m/s. If the density of free electrons in the conductor is 6 * 1024 m-3, what is the current flowing through the conductor?
(Charge on electron = 1.6 * 10-19 C).

• A. 0.45 A
• B. 0.045 A
• C. 0.27 A
• D. 0.31 A
• E. 0.19 A
• Explanation: Current flowing through the conductor is given as
I = neAvc ------------(1)
Putting the values in equation 1 we get
I = 6 * 1024 * 1.6 * 10-19 * 2 * 10-4 * 10-3
I = 0.19 A
Hence, E is the correct answer option.

Q.13

A long straight conductor carries a current of 2 A. What would be the magnetic field at a distance of 0.05 m from the axis of the conductor? (Permeability of free space is 4?? * 10-7 WbA-1m-1)

• A. 8 * 10-6 T
• B. 4 * 10-6 T
• C. 2.5 * 10-6 T
• D. 1.5 * 10-6 T
• E. 6 * 10-6 T
• Explanation: Magnetic field due to along straight conductor is given as
B = (?? / 4??) (2l / a) -----------(1)
Putting the values in equation 1 we get
B = [4 ??*10-7 / 4 ??] * [(2 * 2) / 0.05]
B = 8 * 10-6 T
Hence, A is the correct answer option.

Q.14

A small water drop on a surface is viewed through a glass. If the real depth of the water drop is 15 cm, what will be the apparent depth of the water drop? (Refractive index of glass = 1.5 and refractive index of air = 1)

• A. 5 cm
• B. 7.5 cm
• C. 8.4 cm
• D. 1.5 cm
• E. 10 cm
• Explanation: The apparent depth is given as
glass??air = (??glass / ??air) = (real depth / apparent depth) ----------(1)
Putting the values in equation 1 we get
(1.5 / 1) = (15 / apparent depth)
Apparent depth = 10 cm
Hence, E is the correct answer option.

Q.15

Work function of Nickel is 5.01 eV. What is the threshold frequency for Nickel?
(Planck???s constant = 6.6 * 10-34 Js)

• A. 1.21 * 1015 Hz
• B. 0.56 * 1015 Hz
• C. 4.56 * 1015 Hz
• D. 3.67 * 1014 Hz
• E. 2.23 * 1015 Hz